net: dsa: mv88e6xxx: variable number of databases

Marvell switch chips have different number of address databases.

The code currently only supports models with 4096 databases. Such switch
has dedicated FID registers for ATU and VTU operations. Models with
fewer databases have their FID split in several registers.

List them all but only support models with 4096 databases at the moment.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>