drm/panfrost: Register devfreq cooling and attempt to add Energy Model

Register devfreq cooling device and attempt to register Energy Model. This
will add the devfreq device to the Energy Model framework. It will create
a dedicated and unified data structures used i.e. in thermal framework.
It uses simplified Energy Model, created based on voltage, frequency
and DT 'dynamic-power-coefficient'.

Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20201210143014.24685-6-lukasz.luba@arm.com