net/mlx5e: Create single netdev per SD group

Integrate the SD library calls into the auxiliary_driver ops in
preparation for creating a single netdev for the multiple PFs belonging
to the same SD group.

SD is still disabled at this stage. It is enabled by a downstream patch
when all needed parts are implemented.

The netdev is created whenever the SD group, with all its participants,
are ready. It is later destroyed whenever any of the participating PFs
drops.

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>