ArmVirtPkg/ArmVirtQemu: limit ACPI support to v5.0 and higher

The ACPI spec predates the AARCH64 architecture by 5 versions, so there
is no point in supporting anything below v5.0. So set the PCD that
controls the ACPI table generation to the appropriate value.

Note that the current consumers of this PCD only check whether bit 1
is set or not (i.e., ACPI v1.0b), but this may change in the future,
so let's choose a meaningful value right away.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>