ARM: EXYNOS: allow dt based discovery of mct controller using clocksource_of_init

Add entries to __clksrc_of_table so that Exynos MCT controller is
discoverable using call to clocksource_of_init. With this change,
it would be appropriate to rename the function 'exynos4_timer_init'
as 'mct_init' since it aptly describes this function. Additionally,
the 'init_time' callback of all machine descriptors for exynos
platforms that were previously set to 'exynos4_timer_init' are now
set to either 'mct_init' or 'clocksource_of_init'.

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>