net/mlx5: Add smfs lib to export direct steering API to CT

Add a thin layer that exports selected direct steering (dr) API
which will be used by a ct fs implementation in a following
patch.

Signed-off-by: Paul Blakey <paulb@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>