ASoC: rsnd: Add device tree binding for r8a77990

This patch adds the device tree binding of the r8a77990 SoC.
Signed-off-by: NHiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com>
Signed-off-by: NYoshihiro Kaneko <ykaneko0929@gmail.com>
Signed-off-by: NMark Brown <broonie@kernel.org>

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

@@ -354,6 +354,7 @@ Required properties:
 				    - "renesas,rcar_sound-r8a7795" (R-Car H3)
 				    - "renesas,rcar_sound-r8a7796" (R-Car M3-W)
 				    - "renesas,rcar_sound-r8a77965" (R-Car M3-N)
+				    - "renesas,rcar_sound-r8a77990" (R-Car E3)
 - reg				: Should contain the register physical address.
 				  required register is
 				   SRU/ADG/SSI      if generation1