net/mlx5: Parse module mapping using mlx5_ifc

The assumption that the first byte in the module mapping dword is the
module number shouldn't be hard-coded in the driver, but come from
mlx5_ifc structs.

While at it, fix the incorrect width for the 'rx_lane' and 'tx_lane'
fields.

Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>