dt-bindings: correct marvell orion MDIO binding document

Correct the Marvell Orion MDIO binding document to properly reflect the
cases where an interrupt is present.  Augment the examples to show this.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/marvell-orion-mdio.txt

@@ -7,7 +7,10 @@ interface.
 
 Required properties:
 - compatible: "marvell,orion-mdio"
-- reg: address and length of the SMI register
+- reg: address and length of the MDIO registers.  When an interrupt is
+  not present, the length is the size of the SMI register (4 bytes)
+  otherwise it must be 0x84 bytes to cover the interrupt control
+  registers.
 
 Optional properties:
 - interrupts: interrupt line number for the SMI error/done interrupt
@@ -17,7 +20,7 @@ The child nodes of the MDIO driver are the individual PHY devices
 connected to this MDIO bus. They must have a "reg" property given the
 PHY address on the MDIO bus.
 
-Example at the SoC level:
+Example at the SoC level without an interrupt property:
 
 mdio {
 	#address-cells = <1>;
@@ -26,6 +29,16 @@ mdio {
 	reg = <0xd0072004 0x4>;
 };
 
+Example with an interrupt property:
+
+mdio {
+	#address-cells = <1>;
+	#size-cells = <0>;
+	compatible = "marvell,orion-mdio";
+	reg = <0xd0072004 0x84>;
+	interrupts = <30>;
+};
+
 And at the board level:
 
 mdio {