dt-bindings: net: ravb: Add support for r8a77990 SoC

Add documentation for r8a77990 compatible string to renesas ravb device
tree bindings documentation.
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Rob Herring <robh@kernel.org>

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

@@ -21,6 +21,7 @@ Required properties:
       - "renesas,etheravb-r8a77965" for the R8A77965 SoC.
       - "renesas,etheravb-r8a77970" for the R8A77970 SoC.
       - "renesas,etheravb-r8a77980" for the R8A77980 SoC.
+      - "renesas,etheravb-r8a77990" for the R8A77990 SoC.
       - "renesas,etheravb-r8a77995" for the R8A77995 SoC.
       - "renesas,etheravb-rcar-gen3" as a fallback for the above
 		R-Car Gen3 devices.