net: dsa: mv88e6xxx: remove reserved VLANs

Now that ports isolation is correctly configured when joining or leaving
a bridge, there is no need to rely on reserved VLANs to isolate
unbridged ports anymore. Thus remove them, and disable 802.1Q on setup.

This restores the expected behavior of hardware bridging for systems
without 802.1Q or VLAN filtering enabled.

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