ARM: idle: call idle notifiers before stopping nohz tick

If an idle notifier modifies a timer, calling the notifier after
the sched tick has been stopped may leave the sched tick set too
early.  Move teh idle notifier call before the call to
tick_nohz_stop_sched_tick.

Change-Id: I0db3284bec6d0193bc5e2a57650ab06bd8342319
Signed-off-by: Colin Cross <ccross@android.com>