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

This patch adds support for HDMI audio to the device tree
common to the HiHope RZ/G2M and the HiHope RZ/G2N.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>