mlxsw: trap: Add trap identifiers for mirrored packets

Packets that are mirrored to the CPU port are trapped with one of eight
trap identifiers. Add them.

Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>