arm: mpu: dsb after writing to SCTLR on MPU disable
arm: mpu: dsb after writing to SCTLR on MPU disable

Execute data and instruction sync barriers after writing to SCTLR
to disable the MPU, to ensure the registers are set before
proceeding and that the new changes are seen by the instructions
that follow.

Signed-off-by: Manuel Arguelles <02a481319597bfa86d8bffd931356bede27cabe5@nxp.com>

galak/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr