net: dsa: b53: Plug in VLAN support

Add support for configuration VLANs on B53 devices by implementing the
port VLAN add/del/dump functions. We currently default to a behavior
which is equivalent to having VLAN filtering turned on, where all VLANs
not programmed into the VLAN port-based vector will be discarded on
ingress.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>