net/mlx5e: Add support for devlink-port in non-representors mode

Added devlink_port field to mlx5e_priv structure and a callback to
netdev ops to enable devlink to get info about the port. The port
registration happens at driver initialization.

Signed-off-by: Vladyslav Tarasiuk <vladyslavt@mellanox.com>
Reviewed-by: Moshe Shemesh <moshe@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>