net: stmmac: convert to phylink_get_linkmodes()

Add the MAC speed, duplex and pause capabilities to the phylink_config
structure, and switch stmmac_validate() to use phylink_get_linkmodes()
to generate the mask of supported ethtool link modes.

Tested-by: Wong Vee Khee &lt;vee.khee.wong@linux.intel.com&gt; # Intel EHL Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>