net: dsa: mv88e6xxx: remap existing bridge members

When a local port of a switch chip becomes a member of a bridge group,
we need to reprogram the Cross-chip Port Based VLAN Table (PVT) to allow
existing cross-chip bridge members to egress frames on the new ports.

There is no functional changes yet, since the PVT is still programmed
with all ones, allowing any external port to egress frames locally.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>