net: lan966x: Add offload support for ets

Add ets qdisc which allows to mix strict priority with bandwidth-sharing
bands. The ets qdisc needs to be attached as root qdisc.

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