net: atlantic: adding ethtool physical identification

`ethtool -p eth0` will blink leds helping identify
physical port.

Signed-off-by: Nikita Danilov <ndanilov@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>