drm/doc: Clean up and integrate kerneldoc for drm_gem.c

Fairly incomplete, but at least a start.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/Documentation/DocBook/drm.tmpl b/Documentation/DocBook/drm.tmpl
index f2d0f5b..1cdca9a 100644
--- a/Documentation/DocBook/drm.tmpl
+++ b/Documentation/DocBook/drm.tmpl
@@ -868,7 +868,11 @@
           abstracted from the client in libdrm.
         </para>
       </sect3>
-    </sect2>
+      <sect2>
+        <title>GEM Function Reference</title>
+!Edrivers/gpu/drm/drm_gem.c
+      </sect2>
+      </sect2>
   </sect1>
 
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