net/mlx5: E-switch, Move devlink eswitch ports closer to eswitch

Currently devlink eswitch ports are registered and unregistered by the
representor layer.
However it is better to register them at eswitch layer so that in future
user initiated command port add and delete commands can also
register/unregister devlink ports without depending on representor layer.

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