net/mlx5: Add FEC fields to Port Phy Link Mode (PPLM) reg

Added FEC related fields to PPLM layout.
These fields are needed to set and query FEC policy
for different link speeds.

Signed-off-by: Shay Agroskin <shayag@mellanox.com>
Reviewed-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>