MdeModulePkg DxeCapsuleLibFmp: Update SupportCapsuleImage() for Fake Capsule

MdeModulePkg DxeCapsuleLibFmp: Update SupportCapsuleImage() for Fake Capsule

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1088
Per UEFI spec, the fake capsule image with the header only is a valid case
in QueryCapsuleCpapbilities(). So, SupportCapsuleImage() is updated to
support this case.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Liming Gao <liming.gao@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Jian J Wang <jian.j.wang@intel.com>