net: lan966x: Extend switchdev with mdb support

Extend lan966x driver with mdb support by implementing the switchdev
calls: SWITCHDEV_OBJ_ID_PORT_MDB and SWITCHDEV_OBJ_ID_HOST_MDB.
It is allowed to add both ipv4/ipv6 entries and l2 entries. To add
ipv4/ipv6 entries is not required to use the PGID table while for l2
entries it is required. The PGID table is much smaller than MAC table
so only fewer l2 entries can be added.

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