MdeModulePkg PeiCore: Add PCD to specify PEIM Shadow

MdeModulePkg PeiCore: Add PCD to specify PEIM Shadow

v2 changelog:
Check CurrentPeimHandle to check the matched PeimHandle.
Add check point to ShadowPeiCore based on PCD.

v1 changelog:
PeiCore LoadImage always shadow itself and PEIM on normal boot after
the physical memory is installed. On the emulator platform, the shadow
may be not necessary. To support such usage, new PCD PcdShadowPeimOnBoot
is introduced to specify whether loads PEIM in memory by default.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Liming Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18125 6f19259b-4bc3-4df7-8a09-765794883524