PM: Introduce generic prepare and complete callbacks for subsystems

Introduce generic .prepare() and .complete() power management
callbacks, currently missing, that can be used by subsystems and
power domains and export them.  Provide NULL definitions of all
the generic system sleep callbacks for CONFIG_PM_SLEEP unset.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
diff --git a/include/linux/pm.h b/include/linux/pm.h
index dce7c71..3160648 100644
--- a/include/linux/pm.h
+++ b/include/linux/pm.h
@@ -550,6 +550,16 @@
 	} while (0)
 
 extern int device_pm_wait_for_dev(struct device *sub, struct device *dev);
+
+extern int pm_generic_prepare(struct device *dev);
+extern int pm_generic_suspend(struct device *dev);
+extern int pm_generic_resume(struct device *dev);
+extern int pm_generic_freeze(struct device *dev);
+extern int pm_generic_thaw(struct device *dev);
+extern int pm_generic_restore(struct device *dev);
+extern int pm_generic_poweroff(struct device *dev);
+extern void pm_generic_complete(struct device *dev);
+
 #else /* !CONFIG_PM_SLEEP */
 
 #define device_pm_lock() do {} while (0)
@@ -566,6 +576,15 @@
 {
 	return 0;
 }
+
+#define pm_generic_prepare	NULL
+#define pm_generic_suspend	NULL
+#define pm_generic_resume	NULL
+#define pm_generic_freeze	NULL
+#define pm_generic_thaw		NULL
+#define pm_generic_restore	NULL
+#define pm_generic_poweroff	NULL
+#define pm_generic_complete	NULL
 #endif /* !CONFIG_PM_SLEEP */
 
 /* How to reorder dpm_list after device_move() */
@@ -576,11 +595,4 @@
 	DPM_ORDER_DEV_LAST,
 };
 
-extern int pm_generic_suspend(struct device *dev);
-extern int pm_generic_resume(struct device *dev);
-extern int pm_generic_freeze(struct device *dev);
-extern int pm_generic_thaw(struct device *dev);
-extern int pm_generic_restore(struct device *dev);
-extern int pm_generic_poweroff(struct device *dev);
-
 #endif /* _LINUX_PM_H */