PM: runtime: add missed pm_request_autosuspend

The patch "PM / Runtime: Implement autosuspend support" introduces
"autosuspend" facility for runtime PM, but misses helper function
of pm_request_autosuspend, so add it.
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

include/linux/pm_runtime.h

@@ -164,6 +164,11 @@ static inline int pm_request_resume(struct device *dev)
 	return __pm_runtime_resume(dev, RPM_ASYNC);
 }
 
+static inline int pm_request_autosuspend(struct device *dev)
+{
+	return __pm_runtime_suspend(dev, RPM_ASYNC | RPM_AUTO);
+}
+
 static inline int pm_runtime_get(struct device *dev)
 {
 	return __pm_runtime_resume(dev, RPM_GET_PUT | RPM_ASYNC);