platforms: Add busy wait utils

Some of the mcu-driver-hal tests and examples require utility wait
functions, and these are provided by the bootstrap library delivered by
mcu-driver-hal project. This target is deprecated and will be removed.

Seed each platform with the (streamlined) code from
mcu-driver-hal/bootstrap/src/mbed_wait_api_no_rtos.c.

Signed-off-by: Filip Jagodzinski <filip.jagodzinski@arm.com>