thermal: int340x: Use thermal_zone_for_each_trip()

Modify int340x_thermal_update_trips() to use thermal_zone_for_each_trip()
for walking trips instead of using the trips[] table passed to the
thermal zone registration function.

For this purpose, store active trip point indices in the priv fieids of
the corresponding thermal_trip structures.

No intentional functional impact.

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