net/mlx5e: Advertise globaly supported FEC modes

Ethtool advertise supported link modes on an interface. Per each FEC
mode, query if there is a link type which supports it. If so, add this
FEC mode to the supported FEC modes list. Prior to this patch, ethtool
advertised only the supported FEC modes on the current link type.
Add an explicit mapping between internal FEC modes and ethtool link mode
bits. With this change, adding new FEC modes in the downstream patch
would be easier.

Signed-off-by: Aya Levin <ayal@mellanox.com>
Reviewed-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>