PM/Qos: Expose dev_pm_qos_flags symbol

The dev_pm_qos_flags() will be used in the usb core which could be
compiled as a module. This patch is to export it.
Acked-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NLan Tianyu <tianyu.lan@intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/power/qos.c

@@ -91,6 +91,7 @@ enum pm_qos_flags_status dev_pm_qos_flags(struct device *dev, s32 mask)
 
 	return ret;
 }
+EXPORT_SYMBOL_GPL(dev_pm_qos_flags);
 
 /**
  * __dev_pm_qos_read_value - Get PM QoS constraint for a given device.