Add support for treating unknown PHYs as generic PHYs.

When bringing up u-boot on new boards, PHY support sometimes gets
neglected.  Most PHYs don't really need any special support,
though.  By adding a generic entry that always matches if nothing
else does, we can provide support for "unsupported" PHYs for the
tsec.

The generic PHY driver supports most PHYs, including gigabit.

Signed-off-by: David Updegraff <dave@cray.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>