net: dsa: b53: Create default VLAN entry explicitly

In case CONFIG_VLAN_8021Q is not set, there will be no call down to the
b53 driver to ensure that the default PVID VLAN entry will be configured
with the appropriate untagged attribute towards the CPU port. We were
implicitly relying on dsa_slave_vlan_rx_add_vid() to do that for us,
instead make it explicit.

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