drm: Fix drm_rect documentation

The 'struct' keyword was missing so struct drm_rect documentation never
ended up in the generated docs.

Also move the drm_rect documentations to a new section alognside the
various helper functions and add a short description about the intended
purpose of drm_rect.

v2: Move to new section and add general description

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Documentation/DocBook/drm.tmpl

@@ -1653,8 +1653,6 @@ void intel_crt_init(struct drm_device *dev)
     <sect2>
       <title>KMS API Functions</title>
 !Edrivers/gpu/drm/drm_crtc.c
-!Edrivers/gpu/drm/drm_rect.c
-!Finclude/drm/drm_rect.h
     </sect2>
   </sect1>
 
@@ -2163,6 +2161,12 @@ void intel_crt_init(struct drm_device *dev)
       <title>EDID Helper Functions Reference</title>
 !Edrivers/gpu/drm/drm_edid.c
     </sect2>
+    <sect2>
+      <title>Rectangle Utilities Reference</title>
+!Pinclude/drm/drm_rect.h rect utils
+!Iinclude/drm/drm_rect.h
+!Edrivers/gpu/drm/drm_rect.c
+    </sect2>
   </sect1>
 
   <!-- Internals: vertical blanking -->

include/drm/drm_rect.h

@@ -25,7 +25,14 @@
 #define DRM_RECT_H
 
 /**
- * drm_rect - two dimensional rectangle
+ * DOC: rect utils
+ *
+ * Utility functions to help manage rectangular areas for
+ * clipping, scaling, etc. calculations.
+ */
+
+/**
+ * struct drm_rect - two dimensional rectangle
  * @x1: horizontal starting coordinate (inclusive)
  * @x2: horizontal ending coordinate (exclusive)
  * @y1: vertical starting coordinate (inclusive)