thermal: devfreq_cooling: get a copy of device status

Devfreq cooling needs to now the correct status of the device in order
to operate. Do not rely on Devfreq last_status which might be a stale data
and get more up-to-date values of the load.

Devfreq framework can change the device status in the background. To
mitigate this situation make a copy of the status structure and use it
for internal calculations.

In addition this patch adds normalization function, which also makes sure
that whatever data comes from the device, it is in a sane range.

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