MdeModulePkg/VarCheckPolicyLib: implement standalone MM version

MdeModulePkg/VarCheckPolicyLib: implement standalone MM version

This commit adds the VarCheckPolicyLib that will be able to
execute in the context of standalone MM.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Co-authored-by: Kun Qin <kun.q@outlook.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
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>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>