sched: idle: Do not stop the tick before cpuidle_idle_call()

Make cpuidle_idle_call() decide whether or not to stop the tick.

First, the cpuidle_enter_s2idle() path deals with the tick (and with
the entire timekeeping for that matter) by itself and it doesn't need
the tick to be stopped beforehand.

Second, to address the issue with short idle duration predictions
by the idle governor after the tick has been stopped, it will be
necessary to change the ordering of cpuidle_select() with respect
to tick_nohz_idle_stop_tick().  To prepare for that, put a
tick_nohz_idle_stop_tick() call in the same branch in which
cpuidle_select() is called.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>