ARM: EXYNOS: Initialize the clocks prior to timer initialization

Since the clock initialization should be completed prior to the mct
timer initialization, create a new function 'exynos_init_time' that
first sets up the clock and then invokes the timer initialization
function. The 'init_time' callback in the board files are updated to
invoke this new wrapper function.

Signed-off-by: Thomas Abraham <thomas.abraham@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>