drm/i915: Add a brief description of the VLV display PHY internals

Document the internal structure of the VLV display PHY a bit to help
people understand how the different register blocks relate to each
other.

v2: Add a bit more text
    Make it a DOC: comment, but leave the ascii art out since
    it would get mangled

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chon Ming Lee <chon.ming.lee@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/Documentation/DocBook/drm.tmpl b/Documentation/DocBook/drm.tmpl
index 62573c1..b4f12d4 100644
--- a/Documentation/DocBook/drm.tmpl
+++ b/Documentation/DocBook/drm.tmpl
@@ -2937,6 +2937,10 @@
 	  probing, so those sections fully apply.
         </para>
       </sect2>
+      <sect2>
+        <title>DPIO</title>
+!Pdrivers/gpu/drm/i915/i915_reg.h DPIO
+      </sect2>
     </sect1>
 
     <sect1>