Platform: AN521: Set proper MAIR_ATTR for MPU regions in TFM_LVL 2

MAIR_ATTR for all regions are set as ZERO, which indicates all regions as
Device-nGnRnE. Set proper MAIR_ATTR settings for dedicated MPU regions.
The attributes come from the default memory map. And set the same attribute
for Outer and Inner of Normal memory.

Change-Id: I279e2510746f3b98a8537daf9cdc9ccf63cd14ae
Signed-off-by: Edison Ai <edison.ai@arm.com>