Thermal: Introduce multiple cooling states support

This is because general active cooling devices, like fans,
may have multiple speeds, which can be mapped to different cooling states.

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