To allow overriding of the boot stack size from the Mbed configuration
system, consistently use MBED_CONF_TARGET_BOOT_STACK_SIZE rather than
MBED_BOOT_STACK_SIZE.
Fixes#10319
--legacyalign, --no_legacyalign are deprecated from ARMC6 compiler, in order to
remove deprecated flags all linker files (GCC and IAR as well to have uniformity)
should strictly align to 8-byte boundary
1. Support CMSIS_VECTAB_VIRTUAL feature
2. Reduce the register sync waiting time in LP ticker
3. Adjust the stack and heap size in GCC and IAR toolchains