Add three optional callbacks to the cooling device interface to allow
them to express power.  In addition to the callbacks, add helpers to
identify cooling devices that implement the power cooling device API.

Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Eduardo Valentin <edubezval@gmail.com>
Signed-off-by: Javi Merino <javi.merino@arm.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>