mv643xx_eth: unify ethtool ops for phy'd and phy-less interfaces

It's a waste having two different versions of this structure around
when the differences between ethtool ops for phy'd and phy-less
interfaces are so minor.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>