MdeModulePkg VariablePei: Merge from VariablePei in SecurityPkg

What to do:
1. Merge from VariablePei in SecurityPkg to VariablePei in MdeModulePkg.

Why to do:
1. Remove code duplication and reduce maintenance effort.
The code logic of VariablePei in SecurityPkg is same with VariablePei
in MdeModulePkg.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17756 6f19259b-4bc3-4df7-8a09-765794883524