dt-bindings: ASoC: renesas,rsnd: Add r8a7742 support

Document RZ/G1H (R8A7742) SoC bindings.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Marian-Cristian Rotariu <marian-cristian.rotariu.rb@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1590526904-13855-2-git-send-email-prabhakar.mahadev-lad.rj@bp.renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>