Thermal: build thermal governors into thermal_sys module

The thermal governors are part of the thermal framework,
rather than a seperate feature/module.
Because the generic thermal layer can not work without
thermal governors, and it must load the thermal governors
during its initialization.

Build them into one module in this patch.

This also fix a problem that the generic thermal layer does not
work when CONFIG_THERMAL=m and CONFIG_THERMAL_GOV_XXX=y.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Acked-by: Eduardo Valentin <eduardo.valentin@ti.com>
Acked-by: Durgadoss R <durgadoss.r@intel.com>

Documentation/thermal/sysfs-api.txt

@@ -379,11 +379,3 @@ platform data is provided, this uses the step_wise throttling policy.
 This function serves as an arbitrator to set the state of a cooling
 device. It sets the cooling device to the deepest cooling state if
 possible.
-
-5.5:thermal_register_governor:
-This function lets the various thermal governors to register themselves
-with the Thermal framework. At run time, depending on a zone's platform
-data, a particular governor is used for throttling.
-
-5.6:thermal_unregister_governor:
-This function unregisters a governor from the thermal framework.