ASoC: rsnd: Document R-Car M3-W support

Document support for the sound modules in the Renesas M3-W (r8a7796)
SoC.

No driver update is needed.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/renesas,rsnd.txt

@@ -351,6 +351,7 @@ Required properties:
 				    - "renesas,rcar_sound-r8a7793" (R-Car M2-N)
 				    - "renesas,rcar_sound-r8a7794" (R-Car E2)
 				    - "renesas,rcar_sound-r8a7795" (R-Car H3)
+				    - "renesas,rcar_sound-r8a7796" (R-Car M3-W)
 - reg				: Should contain the register physical address.
 				  required register is
 				   SRU/ADG/SSI      if generation1