rtos: fix SPDX identifiers

rtos: add SPDX identifiers

Harmonise Doxygen comments in drivers, events, platform and rtos dirs ...

When a Doxygen group has been defined (created), all its needed to add
documentation to that group is `\addtogroup`. Since all the information
about the group is preserved, it is not necessary to mention the group
hierarchy again with `\ingroup`. This PR removes unnecessary Doxygen lines
across the `drivers`, `events`, `platform` and `rtos` directories.

It also ensures that new groups are created with `\defgroup` once and
referenced with `\addtogroup` whenever documentation needs to be added to
an existing group.

Change Doxygen groups structure, splitting first by Public/Internal (#11105) ...

* Change Doxygen groups structure, splitting first by Public/Internal

This commit also does the following:
* groups the documentation of related API
* moves `events/internal/equeue.h` to `events/equeue.h`
* merges `events/source/README.md` to `events/README.md`

Drivers/Events/RTOS Public and internal APIs cleanup (#10955) ...

Separate drivers, events, and rtos internal APIs from public APIs.

* Move source files to source subdirs
* Move internal headers to internal subdirs
* Add Doxygen comments for documenting internal and public APIs
* Remove source code from header files in order to remove include pre-processor directives
that included header files not directly used by said header files
* Explicitly include header files instead of implicit inclusions via third-party header files.

Release Notes

This will break user code that was using an internal API as the internal header files have been moved.
This will only break if the user was including the header file using a namespace (i.e #include "foo/bar.h" instead of #include "bar.h"

rtos: NULL -> nullptr ...

Some build errors seen with NULL not being defined. Rather than
add cstddef includes, switch to C++11 nullptr.

Replace deprecated wait calls

RTOS API for bare metal ...

Provide partial RTOS API for bare metal builds - things that
can be done in a single threaded environment.

Allows more code to work in both RTOS and bare metal builds without
change, and in particular gives easy access to the ability to
efficiently wait for something occurring in interrupt.

Available in bare-metal:
* ThisThread
* osThreadFlagsSet to set flags on main thread (can be set from IRQ)
* EventFlags (can be set from IRQ)
* Semaphores (can be released from IRQ)
* Mutex (dummy implementation)

Not useful:
* ConditionVariable (could only be signalled from 2nd thread)
* RtosTimer (calls in a second thread context)
* Thread

Unimplemented:
* Mail, Queue, MemoryPool

Possible future work:
* ConditionVariableCS to act as IRQ signalled ConditionVariable

Fix typos in RTOS doxygen.

rtos: fix astyle

Copy edit RtosTimer.h ...

Copy edit file for active voice.

Add notes about ISR safety to RTOS doxygen

Merge pull request #5372 from SenRamakri/sen_PlatformDoxygenUpdates ...

Doxygen comments fixes

Shrink RTOS classes ...

Various RTOS classes were storing their CMSIS-RTOS creation attribute
structure as a member, when it's not required after construction. Reduce
memory by eliminating this member.

Doxygen comment updates and fixes

Merge pull request #4947 from fkjagodzinski/rtostimer_tests ...

Rtostimer tests

Remove use of internal RTX types ...

Make calls to cmsis-os to get thread state, stack size, and max stack
usage rather than accessing internal RTX data directly. Wrap RTX5
specific code in OS_BACKEND_RTX5.

Also refactor the code to use mbed types rather than RTX types:
os_timer_t -> mbed_rtos_storage_timer_t
os_event_flags_t -> mbed_rtos_storage_event_flags_t
osRtxMutex_t -> mbed_rtos_storage_thread_t

RTOS: RtosTimer: Improve API docs

rtos: Tag non value type as NonCopyable. ...

The types marked are: Mail, MemoryPool, Mutex, Queue, RtosTimer and Semaphore.

Update codebase for CMSIS5/RTX5 ...

Update all of mbed-os to use RTX5.

Renamed files in platform to match source names ...

critical.h     -> mbed_critical.h
sleep.h        -> mbed_sleep.h
toolchain.h    -> mbed_toolchain.h
rtc_time.h     -> mbed_rtc_time.h
semihost_api.h -> mbed_semihost_api.h
wait_api.h     -> mbed_wait_api.h

[RZ/A1H]Support RTX v4.80 for Cortex-A and a few Malloc API (#3470) ...

* [RZ/A1H]Support RTX v4.80 for Cortex-A and a few Malloc API

PR to update RTX to v4.80 for Cortex-A.
In the latest CI test, three tests result in an error. The cause is mainly three points
- Unsupport RTX v4.80 for Cortex-A
- Insufficient stack size of thread defined in test
- A few Lack of Malloc API in GCC
Therefore, I supported to these. For the stack size for test, @Russ already supported in PR #3362.

Reference for issue of test error is here.
https://github.com/ARMmbed/mbed-os/issues/3273

Reference for PR to update RTX for Cortex-M.
https://github.com/ARMmbed/mbed-os/pull/1702

* Revert "[RZ/A1H]Support RTX v4.80 for Cortex-A and a few Malloc API"

This reverts commit e71f79a.

* [RZ/A1H]Support RTX v4.80 for Cortex-A and a few Malloc API

PR to update RTX to v4.80 for Cortex-A.
In the latest CI test, three tests result in an error. The cause is mainly three points
- Unsupport RTX v4.80 for Cortex-A
- Insufficient stack size of thread defined in test
- A few Lack of Malloc API in GCC
Therefore, I supported to these. For the stack size for test, @c1728p9 already supported in PR #3362.

Reference for issue of test error is here.
https://github.com/ARMmbed/mbed-os/issues/3273

Reference for PR to update RTX for Cortex-M.
https://github.com/ARMmbed/mbed-os/pull/1702

Marked the RtosTimer class as deprecated ...

The non-irq timer functionality provided by the RtosTimer is now
duplicated by the EventQueue. See RtosTimer.h for more info.

Add tags to our code

For drivers, events, hal, platform, rtos and mbed.h add one level of path to make sure specific and unique includes files are found.

restructure - Restructured rtos directory