Revert "idle: Move arch_cpu_idle_enter/exit outside tick_nohz_idle_enter/exit"

This reverts commit 0c0e0da6.

Commit 0c0e0da6
(idle: Move arch_cpu_idle_enter/exit outside tick_nohz_idle_enter/exit)
is introduced in hope that a notification callback that schedules a
timer at current jiffy would have its timer function run immediately
before going to idle. This requirement is not met even after moving
the notification outside tick_nohz_idle_enter/exit. That's because timer
list won't be evalulated until next timer tick. Therefore, different
mechanism has to be used instead of relying on timer behavior.

Previous commit also breaks existing guarantee that local interrupts
are disabled in IDLE_START.

Reverting commit 0c0e0da6 to restore
previous idle notification behavior.

Change-Id: Iea8da8b22b26d7a72046a733871e4309c40c5b0c
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>