arch: ARM: Change the march used by cortex-m0 and cortex-m0plus
arch: ARM: Change the march used by cortex-m0 and cortex-m0plus

Use -march=armv6s-m to ensure the svc directive exists

Signed-off-by: Findlay Feng <042dc4512fa3d391c5170cf3aa61e6a638f84342@fengch.me>

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