PM / Runtime: pm_runtime_idle() can be called in atomic context

Add to pm_runtime_idle the list of functions that can be called
in atomic context if pm_runtime_irq_safe() has been called for the
device.
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

Documentation/power/runtime_pm.txt

@@ -478,6 +478,7 @@ pm_runtime_autosuspend_expiration()
 If pm_runtime_irq_safe() has been called for a device then the following helper
 functions may also be used in interrupt context:
 
+pm_runtime_idle()
 pm_runtime_suspend()
 pm_runtime_autosuspend()
 pm_runtime_resume()