dt-bindings: display: add devicetree bindings for pxa300-gcu

This patch adds the binding documentation for the pxa300 gcu.

Signed-off-by: Daniel Mack <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Robert Jarzmik <[e-mail]>
Signed-off-by: Bartlomiej Zolnierkiewicz <[e-mail]>

Documentation/devicetree/bindings/display/marvell,pxa300-gcu.txt

···
+PXA3xx GCU Controller
+---------------------
+
+Required properties:
+ - compatible : "marvell,pxa300-gcu"
+ - reg : should contain the register range (address and length).
+ - interrupts : Controller interrupt.
+ - clocks: phandle to the PXA specific input clock.
+
+Example for PXA300:
+
+	display-controller@54000000 {
+		compatible = "marvell,pxa300-gcu";
+		reg = <0x54000000 0x1000>;
+		interrupts = <39>;
+		clocks = <&clks CLK_PXA300_GCU>;
+	};