dt-bindings: display: renesas: du: document R8A77980 bindings

Document the R-Car V3H (R8A77980) SoC in the R-Car DU bindings; the DU
hardware has the same topology as in the R-Car V3M (R8A77970).

Signed-off-by: Sergei Shtylyov <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Reviewed-by: Laurent Pinchart <[e-mail]>
Signed-off-by: Laurent Pinchart <[e-mail]>

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

···
     - "renesas,du-r8a7796" for R8A7796 (R-Car M3-W) compatible DU
     - "renesas,du-r8a77965" for R8A77965 (R-Car M3-N) compatible DU
     - "renesas,du-r8a77970" for R8A77970 (R-Car V3M) compatible DU
+    - "renesas,du-r8a77980" for R8A77980 (R-Car V3H) compatible DU
     - "renesas,du-r8a77995" for R8A77995 (R-Car D3) compatible DU
 
   - reg: the memory-mapped I/O registers base address and length
···
  R8A7796 (R-Car M3-W)   DPAD 0         HDMI 0         LVDS 0         -
  R8A77965 (R-Car M3-N)  DPAD 0         HDMI 0         LVDS 0         -
  R8A77970 (R-Car V3M)   DPAD 0         LVDS 0         -              -
+ R8A77980 (R-Car V3H)   DPAD 0         LVDS 0         -              -
  R8A77995 (R-Car D3)    DPAD 0         LVDS 0         LVDS 1         -