net: lan966x: Add offload support for tbf

The tbf qdisc allows to attach a shaper on traffic egress on a port or
on a queue. On port they are attached directly to the root and on queue
they are attached on one of the classes of the parent qdisc.

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