drivers: step_wise: Add support for hysteresis temperature

Step wise governor will increase the mitigation when the temperature
goes above a threshold and will decrease the mitigation when the
temperature goes below the threshold. If there is a case where the
temperature is wavering around the threshold, the mitigation will be
applied and removed every iteration, which may not be efficient.
Introduction of hysteresis temperature could avoid this by relaxing
the mitigation only when the temperature goes below this lower
hysteresis value.

Add support for hysteresis temperature in the step wise governor. With
this support, step wise governor will relax the mitigation only
if the temperature goes below the hysteresis temperature.

Change-Id: I6367edaf83e558b2919826342c59346399f53d9b
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>