IB/mlx4: Add support for the port info class for RoCE ports

Report that driver supports IB_PMA_CLASS_CAP_EXT_WIDTH in respond for
IB_MGMT_CLASS_PERF_MGMT mad with IB_PMA_CLASS_PORT_INFO attr id.

Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Matan Barak <matanb@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>