ArmPkg: Fix UncachedFreeAlignedPages in UncachedMemoryAllocationLib

ArmPkg: Fix UncachedFreeAlignedPages in UncachedMemoryAllocationLib

Route both the setting and restoring of cacheability through DXE Services/GCD
and stop using the CPU AP directly.
The patch also removes all references to the CPU AP which eliminates the need
for a library constructor.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Eugene Cohen <eugene@hp.com>
Reviewed-by: Senthil Ramakrishnan <senthil.ramakrishnan@hp.com>
Reviewed-by: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14468 6f19259b-4bc3-4df7-8a09-765794883524