net/mlx5: Generalize QoS operations for nodes and vports

Refactor QoS normalization and rate calculation functions to operate
on mlx5_esw_sched_node, allowing for generalized handling of both
vports and nodes.

Signed-off-by: Carolina Jubran <cjubran@nvidia.com>
Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>