gianfar: Convert gianfar to an of_platform_driver

Does the same for the accompanying MDIO driver, and then modifies the TBI
configuration method.  The old way used fields in einfo, which no longer
exists.  The new way is to create an MDIO device-tree node for each instance
of gianfar, and create a tbi-handle property to associate ethernet controllers
with the TBI PHYs they are connected to.

Signed-off-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -2,8 +2,8 @@
 
 The MDIO is a bus to which the PHY devices are connected.  For each
 device that exists on this bus, a child node should be created.  See
-the definition of the PHY node below for an example of how to define
-a PHY.
+the definition of the PHY node in booting-without-of.txt for an example
+of how to define a PHY.
 
 Required properties:
   - reg : Offset and length of the register set for the device
@@ -21,6 +21,14 @@ Example:
 		};
 	};
 
+* TBI Internal MDIO bus
+
+As of this writing, every tsec is associated with an internal TBI PHY.
+This PHY is accessed through the local MDIO bus.  These buses are defined
+similarly to the mdio buses, except they are compatible with "fsl,gianfar-tbi".
+The TBI PHYs underneath them are similar to normal PHYs, but the reg property
+is considered instructive, rather than descriptive.  The reg property should
+be chosen so it doesn't interfere with other PHYs on the bus.
 
 * Gianfar-compatible ethernet nodes