Memory model for RTOS and No RTOS was initially single stack and heap,
only few targets implemented 2-region RAM model.
2-region RAM model is applied for all toolchains and targets.
GCC: __wrap__sbrk was implemented for 2-region ram model, with switch to 2-region
for all targets, we do not need target specific implementation of this API
Also _sbrk is WEAK function, hence can be over written in target folder for
special cases
Latest cmsis files provide virtual nvic implementation, therefore all nvic
set/get vectors were removed. As the result, we did not reallocate vectors
for mbed SDK. This should fix it for most of the platforms (cortex m0 and
cortex a9 need to provide own if they need it).