thermal: add the support for building the generic thermal as a module

Build the generic thermal driver as module "thermal_sys".

Make ACPI thermal, video, processor and fan SELECT the generic
thermal driver, as these drivers rely on it to build the sysfs I/F.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Acked-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
index 17e71d5..4b62852 100644
--- a/drivers/thermal/Kconfig
+++ b/drivers/thermal/Kconfig
@@ -3,7 +3,7 @@
 #
 
 menuconfig THERMAL
-	bool "Generic Thermal sysfs driver"
+	tristate "Generic Thermal sysfs driver"
 	help
 	  Generic Thermal Sysfs driver offers a generic mechanism for
 	  thermal management. Usually it's made up of one or more thermal
@@ -11,4 +11,4 @@
 	  Each thermal zone contains its own temperature, trip points,
 	  cooling devices.
 	  All platforms with ACPI thermal support can use this driver.
-	  If you want this support, you should say Y here.
+	  If you want this support, you should say Y or M here.