Add multicast filtering support for ICSSG Driver. Multicast addresses will
be updated by __dev_mc_sync() API. icssg_prueth_add_macst () and
icssg_prueth_del_mcast() will be sync and unsync APIs for the driver
respectively.

To add a mac_address for a port, driver needs to call icssg_fdb_add_del()
and pass the mac_address and BIT(port_id) to the API. The ICSSG firmware
will then configure the rules and allow filtering.

If a mac_address is added to port0 and the same mac_address needs to be
added for port1, driver needs to pass BIT(port0) | BIT(port1) to the
icssg_fdb_add_del() API. If driver just pass BIT(port1) then the entry for
port0 will be overwritten / lost. This is a design constraint on the
firmware side.

To overcome this in the driver, to add any mac_address for let's say portX
driver first checks if the same mac_address is already added for any other
port. If yes driver calls icssg_fdb_add_del() with BIT(portX) |
BIT(other_existing_port). If not, driver calls icssg_fdb_add_del() with
BIT(portX).

The same thing is applicable for deleting mac_addresses as well. This
logic is in icssg_prueth_add_mcast / icssg_prueth_del_mcast APIs.
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>