ARM: EXYNOS: move mct driver to drivers/clocksource

Move the multi core timer (mct) driver to from mach-exynos
to drivers/clocksource and update the Kconfig and makefiles.

Cc: Changhwan Youn <chaos.youn@samsung.com>
Signed-off-by: Thomas Abraham <thomas.abraham@linaro.org>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>