ARM: dts: sun[4-7]i: 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: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>