Add ACPI support for Virt Xen ARM and only for aarch64. It gets the ACPI tables through Xen ARM multiboot protocol. Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>