arm64: dts: renesas: r8a77961: salvator-xs: Add HDMI Sound support

This patch enables HDMI Sound on R-Car M3-W+ Salvator-XS board.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87a6y1rtun.wl-kuninori.morimoto.gx@renesas.com


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