net: dsa: bcm_sf2: Add VLAN support

Add support for configuring VLANs on the Broadcom Starfigther2 switch.
This is all done through the bridge vlan facility just like other DSA
drivers.

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