thermal: core: Move some trip processing to thermal_trip_crossed()

Notice that some processing related to trip point crossing carried out
in handle_thermal_trip() and thermal_zone_set_trip_temp() may as well
be done in thermal_trip_crossed(), which allows code duplication to be
reduced, so change the code accordingly.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://patch.msgid.link/1982859.PYKUYFuaPT@rjwysocki.net