thermal: Add sensor API to allow any driver to set thresholds

Sensor API allow drivers to set min or max thresholds and get
notified when the corresponding sensor crosses these thresholds.
The sensor API, uses the THERMAL_TRIP_CONFIGURABLE_HI and
THERMAL_TRIP_CONFIGURABLE_LOW, to set the threshold. The existing
sysfs interfaces will not be affected by the newly added API.

Change-Id: I85d2ae132fc3b7b6d157faf0a7390e31fdc7e6da
Signed-off-by: Praveen Chidambaram <pchidamb@codeaurora.org>