drivers: thermal: step_wise: add support for hysteresis

Step wise governor increases the mitigation level when the temperature
goes above a threshold and will decrease the mitigation when the
temperature falls below the threshold. If it were a case, where the
temperature hovers around a threshold, the mitigation will be applied
and removed at every iteration. This reaction to the temperature is
inefficient for performance.

The use of hysteresis temperature could avoid this ping-pong of
mitigation by relaxing the mitigation to happen only when the
temperature goes below this lower hysteresis value.

Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>
Signed-off-by: Lina Iyer <ilina@codeaurora.org>

drivers: thermal: step_wise: avoid throttling at hysteresis temperature after dropping below it

Signed-off-by: Serge Schneider <serge@raspberrypi.org>

Fix hysteresis support in gov_step_wise.c

Directly get hyst value instead of going through an
optional and, now, unimplemented function.

Signed-off-by: Jürgen Kreileder <jk@blackdown.de>