Platform: MUSCA_A: Set proper MAIR_ATTR for MPU regions

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.

Device-nGnRE : 0b [Outer]0000 [Inner]0100
Code WT   RA : 0b [Outer]1010 [Inner]1010
DATA WBWA RA : 0b [Outer]1111 [Inner]1111

Change-Id: Id1baddc0810681656f2e63d5c9de88bf08187e0a
Signed-off-by: Edison Ai <edison.ai@arm.com>