dsa: Add mdio device support to Marvell switches

Allow Marvell switches to be mdio devices. Currently the driver just
allocate the private structure and detects what device is on the
bus. Later patches will make them register with the DSA framework.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/dsa/marvell.txt

@@ -0,0 +1,27 @@
+Marvell DSA Switch Device Tree Bindings
+---------------------------------------
+
+WARNING: This binding is currently unstable. Do not program it into a
+FLASH never to be changed again. Once this binding is stable, this
+warning will be removed.
+
+If you need a stable binding, use the old dsa.txt binding.
+
+Marvell Switches are MDIO devices. The following properties should be
+placed as a child node of an mdio device.
+
+Required properties:
+- compatible           : Should be one of "marvell,mv88e6085",
+- reg                  : Address on the MII bus for the switch.
+
+Example:
+
+       mdio {
+               #address-cells = <1>;
+               #size-cells = <0>;
+
+               switch0: switch@0 {
+                       compatible = "marvell,mv88e6085";
+                       reg = <0>;
+               };
+       };