[PATCHv2] ACPI-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 <at> intel.com>
---
* This patch depends on v6 of 'writable trip points' patch.
* Fixed an invalid memory reference in create_trip_hyst_attr function.
---
 Documentation/thermal/sysfs-api.txt |    6 +++
 drivers/thermal/thermal_sys.c       |   80 +++++++++++++++++++++++++++++++++++
 include/linux/thermal.h             |    5 ++
 3 files changed, 91 insertions(+), 0 deletions(-)

diff --git a/Documentation/thermal/sysfs-api.txt b/Documentation/thermal/sysfs-api.txt
index 0c7c423..3c8c2f8 100644
--- a/Documentation/thermal/sysfs-api.txt
+++ b/Documentation/thermal/sysfs-api.txt
 <at>  <at>  -121,6 +121,7  <at>  <at>  Thermal zone device sys I/F, created once it's registered:
     |---mode:			Working mode of the thermal zone
     |---trip_point_[0-*]_temp:	Trip point temperature
     |---trip_point_[0-*]_type:	Trip point type
+    |---trip_point_[0-*]_hyst:	Hysteresis value for this trip point

 Thermal cooling device sys I/F, created once it's registered:
 /sys/class/thermal/cooling_device[0-*]: