IB/mlx5: Enable driver uapi commands for flow steering

Expose the mlx5 flow steering parsing trees, exposing the functionality to
user space.

Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>