drm/doc: add new dp helpers into drm DocBook

I didn't bother with documenting the really trivial new "extract
something from dpcd" helpers, but the i2c over aux ch is now
documented a bit.

v2: Clarify the comment for i2c_dp_aux_add_bus a bit.

v3: Fix more spelling fail spotted by Laurent Pinchart.

Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/Documentation/DocBook/drm.tmpl b/Documentation/DocBook/drm.tmpl
index cb8024e..4ee2304 100644
--- a/Documentation/DocBook/drm.tmpl
+++ b/Documentation/DocBook/drm.tmpl
@@ -2105,6 +2105,12 @@
 !Pdrivers/gpu/drm/drm_fb_helper.c fbdev helpers
 !Edrivers/gpu/drm/drm_fb_helper.c
     </sect2>
+    <sect2>
+      <title>Display Port Helper Functions Reference</title>
+!Pdrivers/gpu/drm/drm_dp_helper.c dp helpers
+!Iinclude/drm/drm_dp_helper.h
+!Edrivers/gpu/drm/drm_dp_helper.c
+    </sect2>
   </sect1>
 
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