tests: a fix for ARC and MPU VER 3
tests: a fix for ARC and MPU VER 3

For ARC MPU version 3, the defined partitions are not added to MPU
when appmem_init_app_memory is doning app_bss_zero().

So need to disable mpu first to allow appmem_init_app_memory to
access all partitions.

Signed-off-by: Wayne Ren <d5c6d7c4aa45e53f819f17870783d153a32ba7d0@synopsys.com>

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