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.

Also once Exynos4x12 based platforms support have been removed
the shared exynos-cpufreq driver is no longer needed and can
be deleted.

Based on the earlier work by Thomas Abraham.

Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Thomas Abraham <thomas.ab@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Tested-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Tested-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>