dt-bindings: net: renesas-ravb: Add support for R8A7796 RAVB

Add a new compatible string for the R8A7796 (M3-W) RAVB.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: David S. Miller <davem@davemloft.net>