Change Fat driver to support asynchronous File IO introduced in UEFI spec 2.3.1.D.

Change Fat driver to support asynchronous File IO introduced in UEFI spec 2.3.1.D.

Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
(based on FatPkg commit 063f6e8a9c263bafd52e1226399fc64d6d721dca)

[jordan.l.justen@intel.com: Use script to relicense to 2-clause BSD]
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Acked-by: Mark Doran <mark.doran@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>