net: dsa: mv88e6xxx: program the PVT with all ones

The Cross-chip Port Based VLAN Table (PVT) is currently initialized with
all ones, allowing any external ports to egress frames on local ports.

This commit implements the PVT access functions and programs the PVT
with all ones for the local switch ports only, instead of using the Init
operation. The current behavior is unchanged for the moment.

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>