net: dsa: b53: mark as non-legacy

The B53 driver does not make use of the speed, duplex, pause or
advertisement in its phylink_mac_config() implementation, so it can be
marked as a non-legacy driver.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>