StandaloneMM: Update permissions for Standalone MM drivers memory area

StandaloneMM: Update permissions for Standalone MM drivers memory area

The StandaloneMM image executes in S-EL0 on reference Arm platforms
and is deployed by the trusted firmware as BL32 image. Memory for the
Standalone MM drivers is marked as RW+XN initially, allowing the
drivers to be loaded into the memory. Once loaded, the memory
attributes need to be changed to RO+XN for rodata sections and RO+X
for code sections.

Achieve this through the extra action 'UpdatePeCoffPermissions' to
request the privileged firmware in EL3 to update the permissions.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Sughosh Ganu <sughosh.ganu@arm.com>
Reviewed-by: Achin Gupta <achin.gupta@arm.com>