net: dsa: mv88e6xxx: Enable port policy support on 6097

This chip has support for the same per-port policy actions found in
later versions of LinkStreet devices.

Fixes: f3a2cd32 ("net: dsa: mv88e6xxx: introduce .port_set_policy")
Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
Signed-off-by: David S. Miller <davem@davemloft.net>