net: phylink: allow in-band AN for USXGMII

USXGMII supports passing link information in-band between PHY and MAC PCS,
add it to the list of protocols that support in-band AN mode.

Being a MAC-PHY protocol that can auto-negotiate link speeds up to 10
Gbps, we populate the initial supported mask with the entire spectrum of
link modes up to 10G that PHYLINK supports, and we let the driver reduce
that mask in its .phylink_validate method.

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