The cooling device should be part of the i.MX cpufreq driver, but it
cannot be removed for the sake of DT stability. So turn the cooling
device registration into a separate function and perform the
registration only if the CPU OF node does not have the #cooling-cells
property.

Use of_cpufreq_power_cooling_register in imx_thermal code to link the
cooling device to the device tree node provided.

This makes it possible to bind the cpufreq cooling device to a custom
thermal zone via a cooling-maps entry like:

	cooling-maps {
		map0 {
			trip = <&board_alert>;
			cooling-device = <&cpu0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
		};
	};

Assuming a cpu node exists with label "cpu0" and #cooling-cells
property.
Signed-off-by: Bastian Stender <bst@pengutronix.de>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>