arm64: dts: renesas: Add HiHope RZ/G2M Rev.3.0/4.0 sub board support

The HiHope RZ/G2M sub board sits below the HiHope RZ/G2M Rev.3.0/4.0
main board.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Marian-Cristian Rotariu <marian-cristian.rotariu.rb@bp.renesas.com>
Link: https://lore.kernel.org/r/1593004330-5039-7-git-send-email-prabhakar.mahadev-lad.rj@bp.renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>