PM / OPP: rename header to linux/pm_opp.h

Since Operating Performance Points (OPP) functions are specific
to device specific power management, be specific and rename opp.h
to pm_opp.h

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
index c8c9953..7a7cc74 100644
--- a/include/linux/devfreq.h
+++ b/include/linux/devfreq.h
@@ -15,7 +15,7 @@
 
 #include <linux/device.h>
 #include <linux/notifier.h>
-#include <linux/opp.h>
+#include <linux/pm_opp.h>
 
 #define DEVFREQ_NAME_LEN 16