net/mlx5: SF, Use helpers for allocation and free

Use helper routines for SF id and SF table allocation and free
so that subsequent patch can reuse it for multiple SF function
id range.

Signed-off-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Vu Pham <vuhuong@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>