dt-bindings: interrupt-controller: arm,gic: Support two address and size cells

It should be valid for a GICv2m node, child of a GICv2 node, to use two
cells per reg address and size. The QEMU virt device-tree currently
fails validation because the schema imposes a single address and size
cell. Amend the rule.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220822152224.507497-4-jean-philippe@linaro.org