net: marvell: prestera: implement software MDB entries allocation

Define bridge MDB entry (software entry):
  - entry that get's created upon receiving MDB management events
    (create/delete), that inherently defines a software entry,
    which can be enabled (offloaded to the HW) or disabled (removed
    from HW).
    This separation is done to achieve a better highlevel
    management of HW resources - software MDB entry could exist,
    while it's not necessarily should be configured on the HW.
    For example: by default, the Linux behavior would not replicate
    multicast traffic to multicast group members if there's no
    active multicast router and thus - no actual multicast traffic
    can be received/sent. So, until multicast router appears on the
    system no HW configuration should be applied, although SW MDB entries
    should be tracked.
    Another example would be altering state of 'multicast enabled' on
    the bridge: MC_DISABLED should invoke disabling / clearing multicast
    groups of specified bridge on the HW, yet upon receiving 'multicast
    enabled' event, driver should reconfigure any existing software MDB
    groups on the HW.
    Keeping track of software MDB entries in such way makes it possible
    to properly react on such events.
Define bridge MDB port entry (software entry):
  - entry that helps keeping track (on software - driver - level) of which
    bridge mebemer interface joined any give MDB group;

Co-developed-by: Yevhen Orlov <yevhen.orlov@plvision.eu>
Signed-off-by: Yevhen Orlov <yevhen.orlov@plvision.eu>
Signed-off-by: Oleksandr Mazur <oleksandr.mazur@plvision.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>