arch: arm: mpu: enable WBWA caching on RAM
arch: arm: mpu: enable WBWA caching on RAM

Change the REGION_RAM_ATTR macro to set the cache attributes on RAM
regions to "Outer and inner write-back. Write and read allocate". This
matches the cache attributes used when the MPU is disabled.

Signed-off-by: Aurelien Jarno <bceb368e7f2cb351af47298f32034f0587bbe4a6@aurel32.net>

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