net: phy: Support Marvell 88E1680

Add support for Marvell 88E1680 Integrated Octal
10/100/1000 Mbps Energy Efficient Ethernet Transceiver.

Signed-off-by: Dirk Eibach <dirk.eibach@gdsys.cc>
Signed-off-by: Mario Six <mario.six@gdsys.cc>
Reviewed-by: Stefan Roese <sr@denx.de>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Stefan Roese <sr@denx.de>