do not call sched_clock() too early. Not only might rq->idle
not be set up - but pure per-cpu data might not be accessible
either.

this solves an ia64 early bootup hang with CONFIG_PRINTK_TIME=y.
Tested-by: NTony Luck <tony.luck@gmail.com>
Acked-by: NTony Luck <tony.luck@gmail.com>
Acked-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NIngo Molnar <mingo@elte.hu>