mlxsw: spectrum_switchdev: Attach mid id allocation to HW write

Attach mid getting and releasing mid id to the HW write / remove, and add
a flag to indicate whether the mid is in the HW. It is done because mid id
is also HW index to this mid.
This change allows adding in the following patches the ability to have a
mid in the mdb cache but not in the HW. It will be useful for being able
to disable the multicast.
It means that the mdb is being written / delete to the HW in the mid
allocation / removing function, not after them.

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