thermal/drivers/st: Use generic trip points

The thermal framework gives the possibility to register the trip
points with the thermal zone. When that is done, no get_trip_* ops are
needed and they can be removed.

Convert to the generic trip points

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20221003092602.1323944-21-daniel.lezcano@linaro.org