cpufreq: exynos: move definitions for exynos-cpufreq into drivers/cpufreq/

This moves regarding exynos-cpufreq definitions into drivers/cpufreq/
exynos-cpufreq.h because they are used only for the cpufreq driver.

Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>