Add support to configure multiple prioritized TX traffic
classes with mqprio.

Configure one BD ring per TC for the moment, one netdev
queue per TC.

Signed-off-by: Camelia Groza <camelia.groza@nxp.com>
Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>