net: dsa: mv88e6xxx: add VTU support for 88E6390

The 6390 family of chips use only 2 of the 3 VTU Data registers to pack
the MemberTag and PortState VLAN data. This means that they must be
written or read before or after each VTU/STU operations.

Implement this variant to add support for VTU with such chips. These
chips have a 13th bit for the VID thus set their max_vid to 8191.

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>