CMSIS: Restructure ported CMSIS_5 ...

See docs/adr/0001_cmsis_component_source_structure_recommendations.md
For details information.

Disable write buffering on debug builds. ...

In mbed_start_application() there was a code that was supposed to
set DISDEFWBUF to one when running a debug build. However, this code
was in the wrong place, as this function is only called from
bootloader.

Move the code to correct place so that standalone applications use it
as well.

For the reference of DISDEFWBUF bit, see
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0552a/CHDCBHEE.html

Fix for the missing retrieve error context function call. ...

- Add the function to retrieve error context after a fatal error is called at
   system initialisation for the bare metal profile.

Fixed baremetal heap and stack initialisation. ...

Enabled heap_and_stack test for baremetal.
Added a test to check that global variables are initialised.

In mbed_sdk_boot:
- Added initialisation for mbed_stack_isr_start/size and mbed_heap_start/size for all toolchains.
- ARM toolchain:
   - Added call to mbed_toolchain_init() to initialise global variables.
   - Moved microlib initialisation code from mbed_retarget.cpp to mbed_sdk_boot.c.
- IAR toolchain: there is no equivalent to a software init hook that can be called. __low_level_init() was used but since this function is called before RAM initialisation, it cannot be used to initialize global variables. Defined a new __mbed_init() function called from IAR startup file instead.

Fixing the Mbed OS crash reporting and enable green tea test for bare metal. ...

Added missing mbed_error_initialize function call in bare metal boot code which is used
to retrieve the crash report from RAM in case of any previous abnormal re-boot but this function call is present in RTOS boot code.

fixed astyle issue

Fix for missing os_cb_section ...

-Added the os_cb_section stub to remove the warnings
Incorporated the below review comment
 -Repharase source code comment

Platform: Separate internal APIs from public APIs ...

Also includes:
* rename `mbed_sleep_manager.c` to `mbed_power_mgmt.c` to match its
  header file
* create Doxygen groups for public and internal APIs
* use relative path to include header files where inconsistent
* update references to internal APIs throughout libraries
* update the copyright year for all modified files