Thermal: Introduce simple arbitrator for setting device cooling state

This fixes the problem that a cooling device may be referenced by
by multiple trip points in multiple thermal zones.

With this patch, we have two stages for updating a thermal zone,
1. check if a thermal_instance needs to be updated or not
2. update the cooling device, based on the target cooling state
   of all its instances.

Note that, currently, the cooling device is set to the deepest
cooling state required.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Reviewed-by: Rafael J. Wysocki <rjw@sisk.pl>
Reviewed-by: Eduardo Valentin <eduardo.valentin@ti.com>