idle: Move arch_cpu_idle_enter/exit outside tick_nohz_idle_enter/exit

arch_cpu_idle_enter/exit() send out idle notifications. Notifier
client might want to reschedule timers in the notification. However,
tick_nohz_idle_enter() would have already decided next wake up jiffy,
which could be beyond the client timer's expiration jiffy.

Move arch_cpu_idle_enter/exit() outside tick_nohz_idle_enter/exit()
so timer modification can affect next idle wake up.

Change-Id: Ifcfc06a12b0637b72d0adf0a930cac518eb74bc7
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>