thermal: Modify thermal governors to do nothing for trip points being...

thermal: Modify thermal governors to do nothing for trip points being monitored for falling temperature

For now, thermal governors other than step wise governorr do not support
monitoring of falling temperature. Hence, in case of calls to the governor
for trip points marked as THERMAL_TRIP_MONITOR_FALLING, return doing
nothing.

Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>