arch: arm: define the ARM_SECURE_FIRMWARE option
arch: arm: define the ARM_SECURE_FIRMWARE option

This commit introduces the ARM_SECURE_FIRMWARE k-option,
which indicates that we are building an ARM Secure application.

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

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