[media] media: Media device information query

Create the following ioctl and implement it at the media device level to
query device information.

- MEDIA_IOC_DEVICE_INFO: Query media device information

The ioctl and its data structure are defined in the new kernel header
linux/media.h available to userspace applications.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

Documentation/DocBook/v4l/media-controller.xml

@@ -74,3 +74,13 @@
     pad to a sink pad.</para>
   </section>
 </chapter>
+
+<appendix id="media-user-func">
+  <title>Function Reference</title>
+  <!-- Keep this alphabetically sorted. -->
+  &sub-media-open;
+  &sub-media-close;
+  &sub-media-ioctl;
+  <!-- All ioctls go here. -->
+  &sub-media-ioc-device-info;
+</appendix>