arm64: dts: renesas: hihope-common: Add HDMI support

Add HDMI support to the HiHope RZ/G2[MN] mother board common
dtsi.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>