ARM: shmobile: koelsch-reference: Add DU device to DTS

The DU device has no DT bindings yet, instantiate it as a platform
device for now.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Magnus Damm <damm@opensource.se>
[horms+renesas@verge.net.au: broken out of larger patch that
                             included board changes]
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7791-koelsch.dts

@@ -109,9 +109,14 @@ &extal_clk {
 };
 
 &pfc {
-	pinctrl-0 = <&scif0_pins &scif1_pins>;
+	pinctrl-0 = <&du_pins &scif0_pins &scif1_pins>;
 	pinctrl-names = "default";
 
+	du_pins: du {
+		renesas,groups = "du_rgb666", "du_sync", "du_clk_out_0";
+		renesas,function = "du";
+	};
+
 	scif0_pins: serial0 {
 		renesas,groups = "scif0_data_d";
 		renesas,function = "scif0";