Marvell phy: add configuration of autonegociation for fiber link.

To be correctly initilized, the fiber interface needs
to be configured via autonegociation registers which use
some customs options or registers.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Charles-Antoine Couret <charles-antoine.couret@nexvision.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>