thermal: core: Rework and rename __for_each_thermal_trip()

Rework the currently unused __for_each_thermal_trip() to pass original
pointers to struct thermal_trip objects to the callback, so it can be
used for updating trip data (e.g. temperatures), rename it to
for_each_thermal_trip() and make it available to modular drivers.

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