fec: Add LAN8700 phy support

The i.MX51 babbage board has a FEC ethernet controller with this phy.

In the long term we should resurrect the phylib patches for fec.

Signed-off-by: Amit Kucheria <amit.kucheria@canonical.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>