cpufreq: exynos: remove Exynos4x12 specific cpufreq driver support

cpufreq: exynos: remove Exynos4x12 specific cpufreq driver support

Exynos4x12 based platforms have switched over to use generic
cpufreq driver for cpufreq functionality. So the Exynos
specific cpufreq support for these platforms can be removed.

Based on the earlier work by Thomas Abraham.

Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Cc: Thomas Abraham <thomas.ab@samsung.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>