net: marvell: prestera: add phylink support

For SFP port prestera driver will use kernel
phylink infrastucture to configure port mode based on
the module that has beed inserted

Co-developed-by: Yevhen Orlov <yevhen.orlov@plvision.eu>
Signed-off-by: Yevhen Orlov <yevhen.orlov@plvision.eu>
Co-developed-by: Taras Chornyi <taras.chornyi@plvision.eu>
Signed-off-by: Taras Chornyi <taras.chornyi@plvision.eu>
Signed-off-by: Oleksandr Mazur <oleksandr.mazur@plvision.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>