net: phylink: add helper function to decode USXGMII word
With the new addition of the USXGMII link partner ability constants we
can now introduce a phylink helper that decodes the USXGMII word and
populates the appropriate fields in the phylink_link_state structure
based on them.
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com> Reviewed-by: Russell King <rmk+kernel@armlinux.org.uk> Signed-off-by: David S. Miller <davem@davemloft.net>