ARM: dts: exynos: Remove "cooling-{min|max}-level" for CPU nodes

The "cooling-min-level" and "cooling-max-level" properties are not
parsed by any part of the kernel currently and the max cooling state of
a CPU cooling device is found by referring to the cpufreq table instead.

Remove the unused properties from the CPU nodes.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>