net: txgbe: support copper NIC with external PHY

Wangxun SP chip supports to connect with external PHY (marvell 88x3310),
which links to 10GBASE-T/1000BASE-T/100BASE-T. Add the identification of
media types from subsystem device IDs. For sp_media_copper, register mdio
bus for the external PHY.

Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>