ArmPlatformPkg/MemoryInitPei: AARCH64 fix memory address calculations

ArmPlatformPkg/MemoryInitPei: AARCH64 fix memory address calculations

At least for AARCH64 currently, SystemMemoryTop and FdTop can overflow
while adding the 32-bit PCDs together.  The resulting value loses the
upper 32-bits.  Cast each of the values to EFI_PHYSICAL_ADDRESS size
before doing the addition to prevent erroneous overflow.  There is currently
no 32-bit platform in EDKII open source that will overflow and this change
would not fix that problem anyway.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Garrett Kirkendall <garrett.kirkendall@amd.com>
Reviewed-by: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14675 6f19259b-4bc3-4df7-8a09-765794883524