net: dsa: mv88e6xxx: do not support per-port FID

Since we configure a switch chip through a Linux bridge, and a bridge is
implemented as a VLAN, there is no need for per-port FID anymore.

This patch gets rid of this and simplifies the driver code since we can
now directly map all 4095 FIDs available to all VLANs.

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