Thermal: Add Hysteresis attributes

The Linux Thermal Framework does not support hysteresis
attributes. Most thermal sensors, today, have a
hysteresis value associated with trip points.

This patch adds hysteresis attributes on a per-trip-point
basis, to the Thermal Framework. These attributes are
optionally writable.

Signed-off-by: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>