thermal: trip: Send trip change notifications on all trip updates

The _store callbacks of the trip point temperature and hysteresis sysfs
attributes invoke thermal_notify_tz_trip_change() to send a notification
regarding the trip point change, but when trip points are updated by the
platform firmware, trip point change notifications are not sent.

To make the behavior after a trip point change more consistent,
modify all of the 3 places where trip point temperature is updated
to use a new function called thermal_zone_set_trip_temp() for this
purpose and make that function call thermal_notify_tz_trip_change().

Note that trip point hysteresis can only be updated via sysfs and
trip_point_hyst_store() calls thermal_notify_tz_trip_change() already,
so this code path need not be changed.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>