net: dsa: mv88e6xxx: remove handling for DSA and CPU ports

As we now always use a fixed-link for DSA and CPU ports, we no longer
need the hack in the Marvell code to make this work. Remove it.

This is especially important with the conversion of DSA drivers to
phylink_pcs, as the PCS code only gets called if we are using
phylink for the port.

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