cmake: Add zephyr base address when looking file into soc/
cmake: Add zephyr base address when looking file into soc/

When checking availability of soc/${ARCH}/CMakeLists.txt,
we should use ${ZEPHYR_BASE} as path base.

Fixes #9956

Signed-off-by: Erwan Gouriou <de4d967452b83bb0e37525652734e7d9163b6a4c@linaro.org>

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