Add SPDX license identifier to Arm files ...

Add license identifier to files which Arm owns the copyright to,
and contain either BSD-3 or Apache-2.0 licenses. This is to address
license errors raised by scancode analysis.

TARGET_ARM_FM: Set the heap size and limit

Refactoring memory regions definitions for MPS2_M0 targets ...

* align MPS2_M0 FVP target with other MPS2 targets
* moved memory_zones.h
* chnage the flash_api.c where referencing the old memory_zones
* modify mbed_rtx.h to use the memory_zones definations as INITIAL_SP
* all linker scripts reference the definitions from memory_zones.h
* tool chains use predefined 1K as ISR Stack size
* ARM Complier 5 and GCC will auto calculated heap size
* IAR use predefined 2MiB as heap size

FastModels: add a new parent platform ARM_FM ...

create a new platform folder TARGET_ARM_FM
add general drivers files for FVP_MPS2