thermal: core: Allow trip pointers to be used for cooling device binding

Add new helper functions, thermal_bind_cdev_to_trip() and
thermal_unbind_cdev_from_trip(), to allow a trip pointer to be used for
binding a cooling device to a trip point and unbinding it, respectively,
and redefine the existing helpers, thermal_zone_bind_cooling_device()
and thermal_zone_unbind_cooling_device(), as wrappers around the new
ones, respectively.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>