net/mlx5: Expose max possible SFs via devlink resource

Introduce devlink resource for exposing max possible SFs on mlx5
devices.

For example:
$ devlink resource show pci/0000:00:0b.0
pci/0000:00:0b.0:
  name max_local_SFs size 5 unit entry dpipe_tables none
  name max_external_SFs size 0 unit entry dpipe_tables none

Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>