ARM: vexpress: remove custom .init_time hook

With arch/arm calling of_clk_init(NULL) from time_init(), we can now
remove custom .init_time hooks. The call to versatile_sched_clock_init
is moved to .init_early instead, were it is also for non-DT boards.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Tested-by: Jon Medhurst (Tixy) <tixy@linaro.org>
Acked-by: Pawel Moll <pawel.moll@arm.com>