dsa: lan9303: Migrate to PHYLINK

This patch replaces the adjust_link api with the phylink apis that provide
equivalent functionality.

The remaining functionality from the adjust_link is now covered in the
phylink_mac_link_up api.

Removes:
.adjust_link
Adds:
.phylink_get_caps
.phylink_mac_link_up

Signed-off-by: Jerry Ray <jerry.ray@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>