net: lan966x: Add offload support for taprio

Lan966x switch supports time-based egress shaping in hardware
according to IEEE 802.1Qbv. Add support for TAS configuration on
egress port of lan966x switch.

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