nfp: ethtool: support reporting link modes

Add support for reporting link modes,
including `Supported link modes` and `Advertised link modes`,
via ethtool $DEV.

A new command `SPCODE_READ_MEDIA` is added to read info from
management firmware. Also, the mapping table `nfp_eth_media_table`
associates the link modes between NFP and kernel. Both of them
help to support this ability.

Signed-off-by: Yu Xiao <yu.xiao@corigine.com>
Reviewed-by: Louis Peens <louis.peens@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Alexander Lobakin <alexandr.lobakin@intel.com>
Link: https://lore.kernel.org/r/20221125113030.141642-1-simon.horman@corigine.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>