The current driver code does not accurately report the supported and
advertised link modes.  It basically always assumes the media type
is copper for any particular speed.  Utilize the recently added link
mode mappings to accurately report fully qualified ethtool link modes for
advertised and supported speeds.

If the media type is known, we will report the supported link modes for
that media only.  If the media is not known, we will report all possible
supported link modes.  The user can now specify any supported link modes
(including NRZ and PAM4) to advertise for autoneg.  It used to only accept
copper NRZ modes.
Signed-off-by: Edwin Peer <edwin.peer@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>