PM / Runtime: Add new helper function: pm_runtime_status_suspended()

This boolean function simply returns whether or not the runtime status
of the device is 'suspended'.  Unlike pm_runtime_suspended(), this
function returns the runtime status whether or not runtime PM for the
device has been disabled or not.

Also add entry to Documentation/power/runtime.txt

Signed-off-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

Documentation/power/runtime_pm.txt

@@ -412,6 +412,9 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
     - return true if the device's runtime PM status is 'suspended' and its
       'power.disable_depth' field is equal to zero, or false otherwise
 
+  bool pm_runtime_status_suspended(struct device *dev);
+    - return true if the device's runtime PM status is 'suspended'
+
   void pm_runtime_allow(struct device *dev);
     - set the power.runtime_auto flag for the device and decrease its usage
       counter (used by the /sys/devices/.../power/control interface to