devfreq_cooling: make the structs devfreq_cooling_xxx visible for all

devfreq_cooling: make the structs devfreq_cooling_xxx visible for all

Currently the protection #ifdef CONFIG_DEVFREQ_THERMAL cuts the needed
structures devfreq_cooling_ops and devfreq_cooling_device.
The functions which are supposed to provide the empty implementation complain
about unknown structures.
Similar solution is present in include/linux/devfreq.h.

Reviewed-by: Ørjan Eide <orjan.eide@arm.com>
Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>