[media] media: add a linked list to track interfaces by mdev

The media device should list the interface objects, so add a linked list
for those interfaces in struct media_device.

Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
diff --git a/include/media/media-device.h b/include/media/media-device.h
index 3b14394..51807ef 100644
--- a/include/media/media-device.h
+++ b/include/media/media-device.h
@@ -46,6 +46,7 @@
  * @link_id:	Unique ID used on the last link registered
  * @intf_devnode_id: Unique ID used on the last interface devnode registered
  * @entities:	List of registered entities
+ * @interfaces:	List of registered interfaces
  * @lock:	Entities list lock
  * @graph_mutex: Entities graph operation lock
  * @link_notify: Link state change notification callback
@@ -77,6 +78,7 @@
 	u32 intf_devnode_id;
 
 	struct list_head entities;
+	struct list_head interfaces;
 
 	/* Protects the entities list */
 	spinlock_t lock;