ArmVirtPkg/FdtClientDxe: fix check for size of "reg" properties

ArmVirtPkg/FdtClientDxe: fix check for size of "reg" properties

Currently, the code in FdtClientDxe assumes #address-cells/#size-cells
values of <2>. Since DT "reg" properties always consist of <base, size>
tuples, this means the size of the entire property should always be a
multiple of 16 bytes (i.e, 4 * sizeof(UINT32), not 8. So fix this.

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