FatPkg/FatPei: Use PcdRecoveryFileName PCD.

FatPkg/FatPei: Use PcdRecoveryFileName PCD.

This PCD is used to indicated the recovery file name.
The previous name - FvMain.Fv is hardcoded in FatPei.
It does not make sense to force the name.

Now a platform may use any recovery file name.

Tested-by: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Feng Tian <feng.tian@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>