ASoC: rsnd: Document SoC-specific bindings

The documentation only mentioned the generic fallback compatible
property.
Add the missing SoC-specific compatible properties, which are already in
use.

Also drop a bogus 0x unit-address prefix while we're at it.
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Acked-by: NSimon Horman <horms+renesas@verge.net.au>
Signed-off-by: NMark Brown <broonie@kernel.org>

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

 Renesas R-Car sound
 
 Required properties:
-- compatible			: "renesas,rcar_sound-gen1" if generation1
+- compatible			: "renesas,rcar_sound-<soctype>", fallbacks
+				  "renesas,rcar_sound-gen1" if generation1, and
 				  "renesas,rcar_sound-gen2" if generation2
+				  Examples with soctypes are:
+				    - "renesas,rcar_sound-r8a7790" (R-Car H2)
+				    - "renesas,rcar_sound-r8a7791" (R-Car M2-W)
 - reg				: Should contain the register physical address.
 				  required register is
 				   SRU/ADG/SSI      if generation1
@@ -35,9 +39,9 @@ DAI subnode properties:
 
 Example:
 
-rcar_sound: rcar_sound@0xffd90000 {
+rcar_sound: rcar_sound@ec500000 {
 	#sound-dai-cells = <1>;
-	compatible = "renesas,rcar_sound-gen2";
+	compatible = "renesas,rcar_sound-r8a7791", "renesas,rcar_sound-gen2";
 	reg =	<0 0xec500000 0 0x1000>, /* SCU */
 		<0 0xec5a0000 0 0x100>,  /* ADG */
 		<0 0xec540000 0 0x1000>, /* SSIU */