arm/mpu: Define arm32 system registers

Fix the definition for HPRLAR.
Define the base/limit address registers to access the first 32 protection
regions.

Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@amd.com>
Reviewed-by: Hari Limaye <hari.limaye@arm.com>
Acked-by: Michal Orzel <michal.orzel@amd.com>