net: dsa: b53: Add support for port mirroring

Add support for configuring port mirroring through the cls_matchall
classifier. We do a full ingress or egress capture towards the capture
port. Future improvements could include leveraging the divider to allow
less frames to be captured, as well as matching specific MAC DA/SA.

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