UefiCpuPkg: Shadow microcode patch according to FIT microcode entry.

The existing MpInitLib will shadow the microcode update patches from
flash to memory and this is done by searching microcode region specified
by PCD PcdCpuMicrocodePatchAddress and PcdCpuMicrocodePatchRegionSize.
This brings a limition to platform FW that all the microcode patches must
be placed in one continuous flash space.

This patch shadows microcode update according to FIT microcode entries if
it's present, otherwise it will fallback to original logic (by PCD).

A new featured PCD gUefiCpuPkgTokenSpaceGuid.PcdCpuShadowMicrocodeByFit
is added for enabling/disabling this support.

TEST: Tested on FIT enabled platform.
BZ: https://tianocore.acgmultimedia.com/show_bug.cgi?id=2449



Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Siyuan Fu <siyuan.fu@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>