drivers: thermal: Add low limits monitoring governor

Add low limits monitor governor, which will place a predefined
mitigation action on a cooling device, when the sensor reading falls
below a trip threshold.

This governor will throttle the minimum floor of a cooling device and
doesn't place a maximum scaling cap on a cooling device. So the cooling
devices monitored by this governor should have support to handle the
minimum floor request from the governor. If the cooling device doesn't
support, then the mitigation request from the governor will be ignored
by the thermal sys framework.

Change-Id: I867eb21b18eb0fef42250e21ee2c5920dd547def
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>