powerpc/5121: doc/dts-bindings: update doc of FSL DIU bindings

Update compatible and interrupt properties description.
Furthermore an example for the MPC5121 has been added.
Signed-off-by: Anatolij Gustschin <agust@denx.de>
Acked-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

Documentation/powerpc/dts-bindings/fsl/diu.txt

@@ -4,10 +4,12 @@ The Freescale DIU is a LCD controller, with proper hardware, it can also
 drive DVI monitors.
 
 Required properties:
-- compatible : should be "fsl-diu".
+- compatible : should be "fsl,diu" or "fsl,mpc5121-diu".
 - reg : should contain at least address and length of the DIU register
   set.
-- Interrupts : one DIU interrupt should be describe here.
+- interrupts : one DIU interrupt should be described here.
+- interrupt-parent : the phandle for the interrupt controller that
+  services interrupts for this device.
 
 Example (MPC8610HPCD):
 	display@2c000 {
@@ -16,3 +18,11 @@ Example (MPC8610HPCD):
 		interrupts = <72 2>;
 		interrupt-parent = <&mpic>;
 	};
+
+Example for MPC5121:
+	display@2100 {
+		compatible = "fsl,mpc5121-diu";
+		reg = <0x2100 0x100>;
+		interrupts = <64 0x8>;
+		interrupt-parent = <&ipic>;
+	};