net/mlx5: Refactor vport QoS to use scheduling node structure
Refactor the vport QoS structure by moving group membership and
scheduling details into the `mlx5_esw_sched_node` structure.
This change consolidates the vport into the rate hierarchy by unifying
the handling of different types of scheduling element nodes.
In addition, add a direct reference to the mlx5_vport within the
mlx5_esw_sched_node structure, to ensure that the vport is easily
accessible when a scheduling node is associated with a vport.