mlxsw: spectrum_switchdev: Convert MDB code to use PGT APIs

The previous patches added common APIs for maintaining PGT (Port Group
Table) table. In the legacy model, software did not interact with this
table directly. Instead, it was accessed by firmware in response to
registers such as SFTR and SMID. In the new model, software has full
control over the PGT table using the SMID register.

The configuration of MDB entries is already done via SMID, so the new
PGT APIs can be used also using the legacy model, the only difference is
that MID index should be aligned to bridge model. See a previous patch
which added API for that.

The main changes are:
- MDB code does not maintain bitmap of ports in MDB entry anymore, instead,
  it stores a list of ports with additional information.
- MDB code does not configure SMID register directly anymore, it will be
  done via PGT API when port is first added or removed.
- Today MDB code does not update SMID when port is added/removed while
  multicast is disabled. Instead, it maintains bitmap of ports and once
  multicast is enabled, it rewrite the entry to hardware. Using PGT APIs,
  the entry will be updated also when multicast is disabled, but the
  mapping between {MAC, FID}->{MID} will not appear in SFD register. It
  means that SMID will be updated all the time and disable/enable multicast
  will impact only SFD configuration.
- For multicast router, today only SMID is updated and the bitmap is not
  updated. Using the new list of ports, there is a reference count for each
  port, so it can be saved in software also. For such port,
  'struct mlxsw_sp_mdb_entry.ports_count' will not be updated and the
  port in the list will be marked as 'mrouter'.
- Finally, `struct mlxsw_sp_mid.in_hw` is not needed anymore.
Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>