thermal: devfreq_cooling: add new registration functions with Energy Model

The Energy Model (EM) framework supports devices such as Devfreq. Create
new registration functions which automatically register EM for the thermal
devfreq_cooling devices. This patch prepares the code for coming changes
which are going to replace old power model with the new EM.

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>