net: mvneta: Implement mqprio support

Implement a basic MQPrio support, inserting rules in RX that translate
the TC to prio mapping into vlan prio to queues.

The TX logic stays the same as when we don't offload the qdisc.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>