driver core: create a private portion of struct device

This is to be used to move things out of struct device that no code
outside of the driver core should ever touch.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/base/base.h

@@ -63,6 +63,18 @@ struct class_private {
 #define to_class(obj)	\
 	container_of(obj, struct class_private, class_subsys.kobj)
 
+/**
+ * struct device_private - structure to hold the private to the driver core portions of the device structure.
+ *
+ * @device - pointer back to the struct class that this structure is
+ * associated with.
+ *
+ * Nothing outside of the driver core should ever touch these fields.
+ */
+struct device_private {
+	struct device *device;
+};
+
 /* initialisation functions */
 extern int devices_init(void);
 extern int buses_init(void);