[mii] Separate concepts of MII interface and MII device

We currently have no generic concept of a PHY address, since all
existing implementations simply hardcode the PHY address within the
MII access methods.

A bit-bashing MII interface will need to be provided with an explicit
PHY address in order to generate the correct waveform.  Allow for this
by separating out the concept of a MII device (i.e. a specific PHY
address attached to a particular MII interface).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/velocity.h

@@ -326,7 +326,9 @@ struct velocity_nic {
 	/** Registers */
 	void *regs;
 	/** MII interface */
-	struct mii_interface mii;
+	struct mii_interface mdio;
+	/** MII device */
+	struct mii_device mii;
 	/** Netdev */
 	struct net_device *netdev;