dpaa2-eth: Remove support for changing link settings

We only support fixed-link for now, so there is no point in
offering users the option to change link settings via ethtool.

Functionally there is no change, since firmware prevents us from
changing link parameters anyway.

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>