octeontx2-pf: ethtool fec mode support

Add ethtool support to configure fec modes baser/rs and
support to fecth FEC stats from CGX as well PHY.

Configure fec mode
	- ethtool --set-fec eth0 encoding rs/baser/off/auto
Query fec mode
	- ethtool --show-fec eth0

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>