r8169: use device dependent methods to access the MII registers.

Current mdio_{read/write} needs device specific information to work
correctly with newer chipsets.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Hayes <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>