StandaloneMmPkg: StandaloneMmMemLib: Extends support for X64 architecture

StandaloneMmPkg: StandaloneMmMemLib: Extends support for X64 architecture

This change extends StandaloneMmMemLib library to support X64
architecture. The implementation is ported from MdePkg/Library/SmmMemLib.

Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Sami Mujawar <sami.mujawar@arm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Supreeth Venkatesh <supreeth.venkatesh@arm.com>
Signed-off-by: Kun Qin <kun.q@outlook.com>
Reviewed-by: Jiewen Yao <Jiewen.yao@intel.com>