drm/doc: Integrate drm_modes.c kerneldoc

And clean it up so that there's no kerneldoc warnings. There's still a
lot to do with this one here.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Documentation/DocBook/drm.tmpl

@@ -963,6 +963,10 @@ int max_width, max_height;</synopsis>
 	<para>Mode setting functions.</para>
       </listitem>
     </itemizedlist>
+    <sect2>
+      <title>Display Modes Function Reference</title>
+!Edrivers/gpu/drm/drm_modes.c
+    </sect2>
     <sect2>
       <title>Frame Buffer Creation</title>
       <synopsis>struct drm_framebuffer *(*fb_create)(struct drm_device *dev,