octeontx2-af: advertised link modes support on cgx

CGX supports setting advertised link modes on physical link.
This patch adds support to derive cgx mode from ethtool
link mode and pass it to firmware to configure the same.

Signed-off-by: Christina Jacob <cjacob@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>