dt-bindings: display: renesas: Add R-Car M3-W HDMI TX DT bindings

The M3-W HDMI TX controller seems to be compatible for the H3. No
extension to the DT bindings are needed, add an SoC-specific compatible
string in case differences between the IP versions are found later and
require model-specific handling.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

Documentation/devicetree/bindings/display/bridge/renesas,dw-hdmi.txt

@@ -13,6 +13,7 @@ Required properties:
 
 - compatible : Shall contain one or more of
   - "renesas,r8a7795-hdmi" for R8A7795 (R-Car H3) compatible HDMI TX
+  - "renesas,r8a7796-hdmi" for R8A7796 (R-Car M3-W) compatible HDMI TX
   - "renesas,rcar-gen3-hdmi" for the generic R-Car Gen3 compatible HDMI TX
 
     When compatible with generic versions, nodes must list the SoC-specific