mlxsw: spectrum_span: Add support for global mirroring triggers

Global mirroring triggers are triggers that are only keyed by their
trigger, as opposed to per-port triggers, which are keyed by their
trigger and port.

Such triggers allow mirroring packets that were tail/early dropped or
ECN marked to a SPAN agent.

Implement the previously added trigger operations for these global
triggers. Since such triggers are only supported from Spectrum-2
onwards, have the Spectrum-1 operations return an error.

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