arm64: Call idle notifiers in CPU idle

When CPU idle is enabled, the idle call should also notifiy the
idle_notifier_call_chain of the change in status. Otherwise some
processes will think the CPU is always active.

CRs-Fixed: 677525
Change-Id: Iabd6f617d6835688cf8b482ac1321e5c1deafffd
Signed-off-by: Patrick Cain <pcain@codeaurora.org>