thermal: Make sysfs attributes of cooling devices default attributes

Default attributes are created when the device is registered. Attributes
created after device registration can lead to race conditions, where user space
(e.g. udev) sees the device but not the attributes.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>