Generic bitbanged MDIO library

Previously, bitbanged MDIO was only supported in individual
hardware-specific drivers.  This code factors out the higher level
protocol implementation, reducing the hardware-specific portion to
functions setting direction, data, and clock.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/net/phy/Makefile b/drivers/net/phy/Makefile
index 8885650..3d6cc7b 100644
--- a/drivers/net/phy/Makefile
+++ b/drivers/net/phy/Makefile
@@ -13,3 +13,4 @@
 obj-$(CONFIG_BROADCOM_PHY)	+= broadcom.o
 obj-$(CONFIG_ICPLUS_PHY)	+= icplus.o
 obj-$(CONFIG_FIXED_PHY)		+= fixed.o
+obj-$(CONFIG_MDIO_BITBANG)	+= mdio-bitbang.o