drm/doc: move color management functions under CRTC section

Move drm_color_mgmt function reference from the KMS properties
section to the CRTC abstraction section. This makes the KMS
properties section more readable for user-space developers.
Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Cc: Pekka Paalanen <ppaalanen@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201216202222.48146-5-contact@emersion.fr

Documentation/gpu/drm-kms.rst

@@ -319,6 +319,15 @@ CRTC Functions Reference
 .. kernel-doc:: drivers/gpu/drm/drm_crtc.c
    :export:
 
+Color Management Functions Reference
+------------------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_color_mgmt.c
+   :export:
+
+.. kernel-doc:: include/drm/drm_color_mgmt.h
+   :internal:
+
 Frame Buffer Abstraction
 ========================
 
@@ -499,12 +508,6 @@ Color Management Properties
 .. kernel-doc:: drivers/gpu/drm/drm_color_mgmt.c
    :doc: overview
 
-.. kernel-doc:: drivers/gpu/drm/drm_color_mgmt.c
-   :export:
-
-.. kernel-doc:: include/drm/drm_color_mgmt.h
-   :internal:
-
 Tile Group Property
 -------------------