net: phylink: remove phylink_set_pcs()

As all users of phylink_set_pcs() have now been updated to use the
mac_select_pcs() method, it can be removed from the phylink kernel
API and its functionality moved into phylink_major_config().

Removing phylink_set_pcs() gives us a single approach for attaching
a PCS within phylink.

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