dt-bindings: display: renesas: Add r8a774a1 support

Document RZ/G2M (R8A774A1) SoC bindings.
Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

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

@@ -12,10 +12,12 @@ following device-specific properties.
 Required properties:
 
 - compatible : Shall contain one or more of
+  - "renesas,r8a774a1-hdmi" for R8A774A1 (RZ/G2M) compatible HDMI TX
   - "renesas,r8a7795-hdmi" for R8A7795 (R-Car H3) compatible HDMI TX
   - "renesas,r8a7796-hdmi" for R8A7796 (R-Car M3-W) compatible HDMI TX
   - "renesas,r8a77965-hdmi" for R8A77965 (R-Car M3-N) compatible HDMI TX
-  - "renesas,rcar-gen3-hdmi" for the generic R-Car Gen3 compatible HDMI TX
+  - "renesas,rcar-gen3-hdmi" for the generic R-Car Gen3 and RZ/G2 compatible
+			     HDMI TX
 
     When compatible with generic versions, nodes must list the SoC-specific
     version corresponding to the platform first, followed by the