Rename DEVICE_LOWPOWERTIMER to DEVICE_LPTICKER ...

That's to match DEVICE_USTICKER.

lp_ticker test - provide lp ticker glitch test case ...

Test that lp ticker does not glitch backwards due to an incorrectly implemented ripple counter driver.

Skip higher level ticker tests for targets with stale ticker target specific drivers. ...

Since target specific ticker drivers are not ready also features which uses ticker in upper layers may not work correctly and tests for these features.
We need to disable also failing higher level ticker related tests (by adding check if DEVICE_USTICKER symbol is available and raise #error [NOT_SUPPORTED] if not).

Note:
tests-mbed_drivers-rtc is new and uses us ticker to perform a delay.

lp_us_tickers test - fix count_ticks() function to give the same results on all compilers ...

count_ticks() function counts ticker ticks elapsed during execution of N cycles of empty while loop.
In current version N value (cycles) is given as volatile paramater in order to disable possible compiler optimalisation.
There was a problem with measured time on different compilers and additionally results on ARM compiler were unexpected (the difference beetween measured elapsed ticks for the same number of cycles was to large). This might be caused by the memory access in order to store updated variable in memory. To fix this issue given numer of cycles has been stored into register and register is decremented (no memory access).

With this fix count_ticks(NUM_OF_CYCLES, 1) call returns 2500 +/-1 for us ticker ticks using each compiler (K64F).

lp_us_tickers test - add tolerance to interrupt time. ...

On some platforms (e.g. K64F) different counters are used for time measurement and interrupt generation.
Because of that we should relax interrupt test case and give additional time before checking if interrupt handler has been executed.

lp_us_tickers test - provide counter overflow protection ...

Since according to the ticker requirements min acceptable counter size is 12 bits (low power timer) for which max count is 4095, then all test cases must be executed in this time window.
HAL ticker layer handles overflow and it is not handled in the target ticker drivers.

Adapt K64F lp ticker driver to the new standards. ...

Low power ticker time counter is created based on RTC which is driven by 32KHz clock. Additional low power timer is used to generate interrupts.
We need to adapt driver to operate on ticks instead of us.

Perform the following updates:
- provide lp ticker configuration: 32KHz/32 bit counter.
- lp_ticker_init() routine disables lp ticker interrupts .
- adapt the driver functions to operate on ticks instead us.
- adapt comments.
- add us_ticker_free() routine.

Adapt K64F us ticker driver to the new standards. ...

- provide ticker configuration: 1MHz/32 bit counter.
- us_ticker_init() routine disables interrupts.
- adapt comments.

Enable ticker support for K64F board.

Add lp/us ticker free() function implementation for NRF5

Add free function to lp/us ticker HAL API

Provide fix to the implementation of ticker_overflow_test test case. ...

The intention was to use ticker_overflow_delta equal to 0 for low power ticker tests and ticker_overflow_delta equal to 50 for high frequency ticker tests. Current implementation is invalid since for devices which provide LOW_POWER_TIMER feature delta is equal to 0 and for devices without this feature delta is equal 50.

Modify ticker_init_test() to be consistent with the new requirement.

Modify requirement for the ticker_init function. ...

Current version:
The function ticker_init resets the internal count and disables the ticker interrupt.

Proposed version:
The function ticker_init allows the ticker to keep counting and disables the ticker interrupt.

This is a result of the following discussion:
https://github.com/ARMmbed/mbed-os/pull/5233#pullrequestreview-86677815

Skip higher level ticker tests for targets with stale ticker target specific drivers. ...

Since target specific ticker drivers are not ready also features which uses ticker in upper layers may not work correctly and tests for these features.
We need to disable also failing higher level ticker related tests (by adding check if DEVICE_USTICKER symbol is available and raise #error [NOT_SUPPORTED] if not).

Add DEVICE_RTC symbol check in RTC source files for NCS36510 target.

Disable boards which does not fulfil new ticker standards.

Add minor modifications of lp/us tickers tests desctiption in ticker header files. ...

Add one potential bug to the test description.
Fix test function names to be consistant with desctiption and test header.
Fix typos.

Add tests for ticker HAL API.

Add documentation for the HAL Ticker API ...

Add documentation and test header for the HAL Ticker API.

Remove sleep from rf52 due to failig tests

Implementation of SLEEP feature for Renesas mbed boards ...

I implemented the SLEEP feature for Rnesas mbed boards.
The mainly changing is here.
- hal_sleep()
  To satisfy the mbed specificationm, I implemented this function newly by using "sleep" that is one of low power mode that is incorporated in our hardware(RZ_A1).
  In the "sleep", peripheral and memory state are maintained, and the peripherals continue to work and can generate interrupts.

- hal_deepsleep()
  To satisfy the mbed specificationm, I implemented this function newly by combined using "sleep" and "module standby" that is the low power mode that is incorporated in our hardware(RZ_A1).
  The "module standby" is peripheral module's powerdown.
  Also in case of our "module standby", it need to read register as dummy when access to each register.

Disable `tests-mbed_drivers-timeout` test if USTICKER support is disabled (NRF52_DK).

Disable `tests-mbed_drivers-timerevent` test if USTICKER support is disabled.

tests-mbedmicro-rtos-mbed-systimer: execute sleep/deepsleep test cases only when SLEEP support is enabled.

Disable SLEEP support for MAX32630FTHR and KW41Z platforms. ...

These platforms are not consistent with the new sleep standards.

ARM_CM3DS_MPS2: add protection to lp_ticker.c. ...

Compile this file only when DEVICE_LOWPOWERTIMER is defined.

tests-mbed_hal-sleep: decrease delay when testing if us ticker is disabled in deep-sleep mode. ...

This is done because of possible limitations of lowpower ticker freq/width.

tests-mbed_hal-sleep: fix formatting.

tests-mbed_hal-sleep: remove unused variable.