sched: add config flexibility to TC queue sizes

Add support for zero queue sizes of the traffic classes. The queues
which are not used can be set to zero size. This helps in reducing
memory footprint of the hierarchical scheduler.

Signed-off-by: Jasvinder Singh <jasvinder.singh@intel.com>
Signed-off-by: Abraham Tovar <abrahamx.tovar@intel.com>
Signed-off-by: Lukasz Krakowiak <lukaszx.krakowiak@intel.com>