Revert "MdePkg/ProcessorBind.h AARCH64: limit MAX_ADDRESS to 48 bits"

Revert "MdePkg/ProcessorBind.h AARCH64: limit MAX_ADDRESS to 48 bits"

This reverts commit 82379bf6603274e81604d5a6f6bb14bdde616286.

On AArch64, we can only use 48 address bits while running in UEFI,
while the GCD and UEFI memory maps may describe up to 52 bits of
physical address space. For this reason, MAX_ADDRESS was reduced
to 48 bits, to ensure that the firmware does not inadvertently
attempt to allocate memory that we cannot access.

However, MAX_ADDRESS is used in runtime drivers as well, and
runtime drivers may deal with kernel virtual addresses, which have
bits [63:48] set. In fact, the OS may be running with 64 KB pages
and pass addresses into the runtime services that use up to 52
bits of address space, either with the top bits set or cleared,
even if the physical address space does not extend beyond 48 bits.

In summary, changing MAX_ADDRESS is a mistake, and needs to be
reverted.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>