mlxsw: spectrum_fid: Introduce emulated 802.1Q FIDs

The driver uses 802.1Q FIDs when offloading a VLAN-aware bridge.
Unfortunately, it is not possible to assign a VNI to such FIDs, which
prompts the driver to forbid the enslavement of VxLAN devices to a
VLAN-aware bridge.

Workaround this hardware limitation by creating a new family of FIDs,
emulated 802.1Q FIDs. These FIDs are emulated using 802.1D FIDs, which
can be assigned a VNI.

The downside of this approach is that multiple {Port, VID}->FID entries
are required, whereas only a single VID->FID is required with "true"
802.1Q FIDs.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>