mlxsw: spectrum_fid: Maintain {port, VID}->FID mappings

In the unified bridge model, FID classification mappings (e.g., {Port,
VID}->FID) and layer 3 egress VID classification mappings (i.e., {eRIF,
ePort}->VID) will need to be updated when a RIF is configured on top of
a FID. This requires the driver to be aware of all the {Port, VID} pairs
mapped to a FID.

To that end, extend the FID structure with a linked list of {Port, VID}
pairs. Add an entry to the list when a {Port, VID} is mapped to a FID
and remove it upon unmap.

Keep the list sorted by local port as it will be useful for {eRIF,
ePort}->VID mappings via REIV register in the future.

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>