test: kernel: userspace: add include for arm core mpu
test: kernel: userspace: add include for arm core mpu

In the wake of dfa7a354ff2a31fea8614b3876b051aadc30b242, where
the inclusions for MPU APIs were clean-up, we need to directly
include arm_core_mpu_dev.h in the userspace test suite, which
invokes arm_core_mpu_enable/disable(), directly. The same is
already done for ARC MPU.

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

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