ARM: Exynos: switch to using generic cpufreq driver for Exynos5250

ARM: Exynos: switch to using generic cpufreq driver for Exynos5250

The new CPU clock type allows the use of generic CPUfreq driver.
Switch Exynos5250 to using generic cpufreq driver.

Changes by Bartlomiej:
- split Exynos5250 support from the original patch

Cc: Tomasz Figa <tomasz.figa@gmail.com>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Cc: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>