thermal/drivers/cpu_cooling: Rename to cpufreq_cooling

As we introduced the idle injection cooling device called
cpuidle_cooling, let's be consistent and rename the cpu_cooling to
cpufreq_cooling as this one mitigates with OPPs changes.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>
Link: https://lore.kernel.org/r/20191219225317.17158-3-daniel.lezcano@linaro.org