arch: arm: mpu: implement API for memory domains in ARM (core) MPU

This commit updates the ARM Core MPU API for memory domains,
to align with the principle of de-coupling the partitioning
and the access attribution with the architecture-specific
MPU driver implementation.

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