net: dsa: qca8k: add support for port fast aging

The switch supports fast aging by flushing any rule in the ARL
table for a specific port.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>