ARM: EXYNOS: Move arm core power down clock to exynos5250 common clock

Now with common clock support added for exynos5250 it is necessary to
move this code to exynos5250 common clock driver as clock registers
should be handled there. This change is tested in exynos5250 based
arndale platform.

Cc: Abhilash Kesavan <a.kesavan@samsung.com>
Cc: Thomas Abraham <thomas.abraham@linaro.org>
Acked-by: Kukjin Kim <kgene.kim@samsugn.com>
Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
[t.figa: Rebased onto current kernel sources.]
Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>