net: dsa: felix: allow configurable phylink_mac_config

If a user of the Felix driver has a port running in SGMII / QSGMII mode, it
will need to utilize phylink_mac_config(). Add this configurability.

Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Signed-off-by: David S. Miller <davem@davemloft.net>