net: mscc: ocelot: filter out ocelot SoC specific PCS config from common path

The adjust_link routine should be generic enough to be (re)used by
any SoC that integrates a switch core compatible with the Ocelot
core switch driver.  Currently all configurations are generic except
for the PCS settings that are SoC specific.  Move these out to the
Ocelot SoC/board instance.

Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>