mlxsw: spectrum: Separate bc and mc floods

Break the bm (broadcast-multicast) into two tables, one for broadcast
(and link local multicast that behaves like bc) and one for unknown
multicasts.
Add a bool into mlxsw_sp_port named mc_flood that reflect the value this
port should have in the mc flood table (currently, always 1);

Signed-off-by: Nogah Frankel <nogahf@mellanox.com>
Signed-off-by: Yotam Gigi <yotamg@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>