ArmPkg: Expand AArch64 address width to 48 bits

ArmPkg: Expand AArch64 address width to 48 bits

The VA address space has a maximum address width of 48 bits in
AArch64 state; 48 bits address width limit will provide better
compatibility than 40 bits for future CPU.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Heyi Guo <heyi.guo@linaro.org>
Reviewed-by: Olivier Martin <Olivier.Martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17526 6f19259b-4bc3-4df7-8a09-765794883524