ravb: document R8A77970 bindings

R-Car V3M (R8A77970) SoC also has the R-Car gen3 compatible EtherAVB
device, so document  the SoC specific bindings.
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/renesas,ravb.txt

@@ -17,6 +17,7 @@ Required properties:
 
       - "renesas,etheravb-r8a7795" for the R8A7795 SoC.
       - "renesas,etheravb-r8a7796" for the R8A7796 SoC.
+      - "renesas,etheravb-r8a77970" for the R8A77970 SoC.
       - "renesas,etheravb-rcar-gen3" as a fallback for the above
 		R-Car Gen3 devices.
 
@@ -40,7 +41,7 @@ Optional properties:
 - interrupt-parent: the phandle for the interrupt controller that services
 		    interrupts for this device.
 - interrupt-names: A list of interrupt names.
-		   For the R8A779[56] SoCs this property is mandatory;
+		   For the R-Car Gen 3 SoCs this property is mandatory;
 		   it should include one entry per channel, named "ch%u",
 		   where %u is the channel number ranging from 0 to 24.
 		   For other SoCs this property is optional; if present