Moves StandaloneMmCoreEntryPoint for X64 to MdePkg to live with
the other entry point libs. It does not move the ARM64 version,
as this was just moved to ArmPkg due to its heavy coupling with
ArmPkg code. This will need to be revisited when dynamic stack
cookie support is added to ARM64 StMM.
This commit just adds the library in MdePkg, a separate commit
will remove it from StandaloneMmPkg to make it easier to consume.
Signed-off-by: Oliver Smith-Denny <osde@microsoft.com>
885bcca649