drm/doc: Move hdmi infoframe docs

.. next to all the other sink helpers. The rect library is more used
for handling plane clipping, so belongs to those imo.
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190130163006.28945-1-daniel.vetter@ffwll.ch

Documentation/gpu/drm-kms-helpers.rst

@@ -296,18 +296,6 @@ SCDC Helper Functions Reference
 .. kernel-doc:: drivers/gpu/drm/drm_scdc_helper.c
    :export:
 
-Rectangle Utilities Reference
-=============================
-
-.. kernel-doc:: include/drm/drm_rect.h
-   :doc: rect utils
-
-.. kernel-doc:: include/drm/drm_rect.h
-   :internal:
-
-.. kernel-doc:: drivers/gpu/drm/drm_rect.c
-   :export:
-
 HDMI Infoframes Helper Reference
 ================================
 
@@ -322,6 +310,18 @@ libraries and hence is also included here.
 .. kernel-doc:: drivers/video/hdmi.c
    :export:
 
+Rectangle Utilities Reference
+=============================
+
+.. kernel-doc:: include/drm/drm_rect.h
+   :doc: rect utils
+
+.. kernel-doc:: include/drm/drm_rect.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_rect.c
+   :export:
+
 Flip-work Helper Reference
 ==========================