AmpereAltraPkg: Support UEFI non-volatile variable

This change supports storing the UEFI non-volatile varibles on the
Flash through below modules:
* FlashPei driver helps to restore the saved variables from
  flash on each boot.
* FlashFvbDxe driver provides the implementation for the
  gEfiFirmwareVolumeBlock protocol

Cc: Thang Nguyen <thang@os.amperecomputing.com>
Cc: Chuong Tran <chuong@os.amperecomputing.com>
Cc: Phong Vo <phong@os.amperecomputing.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>

Signed-off-by: Nhi Pham <nhi@os.amperecomputing.com>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>