ST boards: Fix sleep tracing ...

Prevent singleton lock if the RTOS is not yet ready.

lp_ticker is used during the RTOS initialization process.
ST lp_ticker implementation calls sleep functions
which in turn attempts to print to the console when sleep tracing
is enabled. Console initialization attempts to lock the singleton mutex.

psa: Init IPC, Mailbox and Non-secure Interface ...

These changes are for TFM_DUALCPU and TFM_V8M platforms.
The initialization happens after mbed-os kernel is kicked off and
when the thread is up and running.

We are initializing the following for TFM_DUALCPU platforms:
* IPC Interrupts for syncing multi-core platforms.
* NS Mailbox to receive messages.
* NS interface.

We are only initializing Non-secure interface for TFM_V8M platforms.

mbed_tfm_init() in tfm_mbed_boot.c overrides the WEAK mbed_tfm_init()
for a specific platform.

Signed-off-by: Vikas Katariya <vikas.katariya@arm.com>

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.

Move TARGET directories to source