UefiCpuPkg/PiSmmCpu: Remove hardcode 48 address size limitation

UefiCpuPkg/PiSmmCpu: Remove hardcode 48 address size limitation

5-level paging can be enabled on CPU which supports up to 52 physical
address size. But when the feature was enabled, the 48 address size
limit was not removed and the 5-level paging testing didn't access
address >= 2^48. So the issue wasn't detected until recently an
address >= 2^48 is accessed.

Signed-off-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>