In preparation for supporting multiple MDIO busses, pass the mii_bus
structure to all PHY operations. It will in future then be clear on
which MDIO bus the operation should be performed.

For reads/write from phylib, the mii_bus is readily available. However
some internal code also access the PHY, e.g. for EEE and SERDES. Make
this code use the one and only currently available MDIO bus.
Signed-off-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>