mlxsw: spectrum_span: Prepare for global mirroring triggers

Currently, a SPAN agent can only be bound to a per-port trigger where
the trigger is either an incoming packet (INGRESS) or an outgoing packet
(EGRESS) to / from the port.

The subsequent patch will introduce the concept of global mirroring
triggers. The binding / unbinding of global triggers is different than
that of per-port triggers. Such triggers also need to be enabled /
disabled on a per-{port, TC} basis and are only supported from
Spectrum-2 onwards.

Add trigger operations that allow us to abstract these differences. Only
implement the operations for per-port triggers. Next patch will
implement the operations for global triggers.

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>