net: dsa: microchip: ksz8795: add phylink support

This patch adds the phylink support to the ksz8795 driver to provide
configuration exceptions on quirky KSZ8863 and KSZ8873 ports.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>