cpufreq: exynos: Use device tree to determine if cpufreq cooling should be registered

With thermal subsystem rework it is necessary to tune current cpufreq code
to use cpu frequency change as a potential cooling device.

Now the cpu cooling device is registered only when proper nodes and properties
are available in device tree. Lack of them, however, will not prevent
cpufreq for normal operation.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>