Build FatPkg for AArch64 platforms.

Build FatPkg for AArch64 platforms.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <Olivier.Martin@arm.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
(based on FatPkg commit a952f09e53b2eda00370cd987229083daa496b13)

[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: Laszlo Ersek <lersek@redhat.com>
Acked-by: Leif Lindholm <leif.lindholm@arm.com>