cpufreq: qoriq: Don't show cooling device messages if THERMAL_OF undefined

When THERMAL_OF is undefined the cooling device messages should not be
shown. -ENOSYS is returned from of_cpufreq_cooling_register() when
THERMAL_OF is undefined.

Signed-off-by: Jia Hongtao <hongtao.jia@nxp.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>