MdeModulePkg DxeCore: Add FVH signature check before VerifyFvHeaderChecksum in FwVol.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>


git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16200 6f19259b-4bc3-4df7-8a09-765794883524