net: dsa: microchip: ksz8: Implement add/del_fdb and use static MAC table operations

Add support for add/del_fdb operations and utilize the refactored static
MAC table code. This resolves kernel warnings caused by the lack of fdb
add function support in the current driver.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>