PM / devfreq: add devfreq_suspend/resume() functions

This patch adds implementation for global suspend/resume for
devfreq framework. System suspend will next use these functions.

Suggested-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Suggested-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Lukasz Luba <l.luba@partner.samsung.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
index d985199..fbffa74 100644
--- a/include/linux/devfreq.h
+++ b/include/linux/devfreq.h
@@ -205,6 +205,9 @@ extern void devm_devfreq_remove_device(struct device *dev,
 extern int devfreq_suspend_device(struct devfreq *devfreq);
 extern int devfreq_resume_device(struct devfreq *devfreq);
 
+extern void devfreq_suspend(void);
+extern void devfreq_resume(void);
+
 /**
  * update_devfreq() - Reevaluate the device and configure frequency
  * @devfreq:	the devfreq device
@@ -331,6 +334,9 @@ static inline int devfreq_resume_device(struct devfreq *devfreq)
 	return 0;
 }
 
+static inline void devfreq_suspend(void) {}
+static inline void devfreq_resume(void) {}
+
 static inline struct dev_pm_opp *devfreq_recommended_opp(struct device *dev,
 					   unsigned long *freq, u32 flags)
 {