thermal: thermal_of: Extend thermal dt driver to support bi-directional...

thermal: thermal_of: Extend thermal dt driver to support bi-directional monitoring of a thermal trip point.

Introduce of_thermal_get_trip_monitor_type to return the direction
of monitoring of a thermal trip point. Also translate the DT information
regarding trip point monitor direction into the thermal framework.

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