thermal: core: Introduce .trip_crossed() callback for thermal governors

Introduce a new thermal governor callback called .trip_crossed()
that will be invoked whenever a trip point is crossed by the zone
temperature, either on the way up or on the way down.

The trip crossing direction information will be passed to it and if
multiple trips are crossed in the same direction during one thermal zone
update, the new callback will be invoked for them in temperature order,
either ascending or descending, depending on the trip crossing
direction.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>