cpufreq: Use of_property_present()

Use of_property_present() to test for property presence rather than
of_(find|get)_property(). This is part of a larger effort to remove
callers of of_find_property() and similar functions. of_find_property()
leaks the DT struct property and data pointers which is a problem for
dynamically allocated nodes which may be freed.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>