net: lan966x: Extend switchdev with fdb support

Extend lan966x driver with fdb support by implementing the switchdev
calls SWITCHDEV_FDB_ADD_TO_DEVICE and SWITCHDEV_FDB_DEL_TO_DEVICE.

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