net: dsa: mt7530: add support for port mirroring

Add support for configuring port mirroring through the cls_matchall
classifier. We do a full ingress and/or egress capture towards a
capture port.
MT7530 supports one monitor port and multiple mirrored ports.

Signed-off-by: DENG Qingfang <dqfext@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>