net: dsa: mv88e6xxx: convert 88e6185 to phylink_pcs

Convert the 88E6185 SERDES code to use the phylink_pcs infrastructure.

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