net/mlx5: E-switch, Add eswitch helpers for SF vport

Add helpers to enable/disable eswitch port, register its devlink port and
load its representor.

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