openfirmware: Add OF phylib support code

Add support for parsing the device tree for PHY devices on an MDIO bus.
Currently many of the PowerPC ethernet drivers are open coding a solution
for reading data out of the device tree to find the correct PHY device.
This patch implements a set of common routines to:

a) let MDIO bus drivers register phy_devices described in the tree, and
b) let MAC drivers find the correct phy_device via the tree.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/of/Makefile b/drivers/of/Makefile
index 4c3c6f8..bdfb5f5 100644
--- a/drivers/of/Makefile
+++ b/drivers/of/Makefile
@@ -3,3 +3,4 @@
 obj-$(CONFIG_OF_GPIO)   += gpio.o
 obj-$(CONFIG_OF_I2C)	+= of_i2c.o
 obj-$(CONFIG_OF_SPI)	+= of_spi.o
+obj-$(CONFIG_OF_MDIO)	+= of_mdio.o