ArmPkg: Export SetMemoryRegionAttribute in ArmMmuLib

Arm CCA requires the software in a Realm to treat the most
significant bit of an IPA as a protection attribute. To
enable/disable sharing of memory regions with the host, the
protection attribute needs to be set/cleared accordingly.

Instead of implementing the functionality to Set/Clear the
protection attribute in ArmMmuLib, defer this to an Arm CCA
specific library so that additional dependencies for
ArmMmuLib can be avoided.

Therefore, export the SetMemoryRegionAttribute () in
ArmMmuLib so that the Realm software can configure the
protection attribute.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>