hwmon: (cros_ec) register fans into thermal framework cooling devices

Register fans connected under EC as thermal cooling devices as well, so
these fans can then work with the thermal framework.

During the driver probing phase, we will also try to register each fan
as a thermal cooling device based on previous probe result (whether the
there are fans connected on that channel, and whether EC supports fan
control). The basic get max state, get current state, and set current
state methods are then implemented as well.

Signed-off-by: Sung-Chi Li <lschyi@chromium.org>
Acked-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20250911-cros_ec_fan-v6-3-a1446cc098af@google.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>