net: lan966x: Add offload support for mqprio

Implement mqprio qdisc support using tc command.
The HW supports 8 priority queues from highest (7) to lowest (0).

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>