net: pcs: xpcs: convert to phylink_pcs_ops

Since all the remaining members of struct mdio_xpcs_ops have direct
equivalents in struct phylink_pcs_ops, it is about time we remove it
altogether.

Since the phylink ops return void, we need to remove the error
propagation from the various xpcs methods and simply print an error
message where appropriate.

Since xpcs_get_state_c73() detects link faults and attempts to reset the
link on its own by calling xpcs_config(), but xpcs_config() now has a
lot of phylink arguments which are not needed and cannot be simply
fabricated by anybody else except phylink, the actual implementation has
been moved into a smaller xpcs_do_config().

The const struct mdio_xpcs_ops *priv->hw->xpcs has been removed, so we
need to look at the struct mdio_xpcs_args pointer now as an indication
whether the port has an XPCS or not.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>