arch: arm: include GCC -mcmse compile option for secure firmware
arch: arm: include GCC -mcmse compile option for secure firmware

Make GCC compile with the -mcmse compile option, if we are
building a Secure firmware. The option will make Security
Extensions for secure executables available, and will set
the corresponding compile-time indicator flag, accordingly:
(i.e. __ARM_FEATURE_CMSE=3).

Signed-off-by: Ioannis Glaropoulos <5921cc8bab7e1d4329f52fd8f6268f9692e3de80@nordicsemi.no>

zephyrproject-rtos/zephyr,nashif/zephyr,Vudentz/zephyr,kraj/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,punitvara/zephyr,galak/zephyr,galak/zephyr,ldts/zephyr,punitvara/zephyr,Vudentz/zephyr,kraj/zephyr,finikorg/zephyr,kraj/zephyr,ldts/zephyr,explora26/zephyr,punitvara/zephyr,explora26/zephyr,finikorg/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,nashif/zephyr,finikorg/zephyr,punitvara/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,Vudentz/zephyr,kraj/zephyr,finikorg/zephyr,nashif/zephyr,galak/zephyr,ldts/zephyr,nashif/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,punitvara/zephyr,kraj/zephyr