dt-bindings: display: renesas: du: Document R8A77970 bindings

Document the R-Car V3M (R8A77970) SoC in the R-Car DU bindings.
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

Documentation/devicetree/bindings/display/renesas,du.txt

@@ -13,6 +13,7 @@ Required Properties:
     - "renesas,du-r8a7794" for R8A7794 (R-Car E2) compatible DU
     - "renesas,du-r8a7795" for R8A7795 (R-Car H3) compatible DU
     - "renesas,du-r8a7796" for R8A7796 (R-Car M3-W) compatible DU
+    - "renesas,du-r8a77970" for R8A77970 (R-Car V3M) compatible DU
 
   - reg: the memory-mapped I/O registers base address and length
 
@@ -57,6 +58,7 @@ corresponding to each DU output.
  R8A7794 (R-Car E2)   DPAD 0         DPAD 1         -              -
  R8A7795 (R-Car H3)   DPAD 0         HDMI 0         HDMI 1         LVDS 0
  R8A7796 (R-Car M3-W) DPAD 0         HDMI 0         LVDS 0         -
+ R8A77970 (R-Car V3M) DPAD 0         LVDS 0         -              -
 
 
 Example: R8A7795 (R-Car H3) ES2.0 DU