drm/bridge: Add documentation sections

The bridge documentation overview is quite packed already, and we'll add
some more documentation that isn't part of an overview at all.

Let's add some sections to the documentation to separate each bits.

Reviewed-by: Andrzej Hajda <[e-mail]>
Reviewed-by: Sam Ravnborg <[e-mail]>
Signed-off-by: Maxime Ripard <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

Documentation/gpu/drm-kms-helpers.rst

···
 .. kernel-doc:: drivers/gpu/drm/drm_bridge.c
    :doc: overview
 
+Display Driver Integration
+--------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
+   :doc: display driver integration
+
 Bridge Operations
 -----------------
 

drivers/gpu/drm/drm_bridge.c

···
  * Chaining multiple bridges to the output of a bridge, or the same bridge to
  * the output of different bridges, is not supported.
  *
+ * &drm_bridge, like &drm_panel, aren't &drm_mode_object entities like planes,
+ * CRTCs, encoders or connectors and hence are not visible to userspace. They
+ * just provide additional hooks to get the desired output at the end of the
+ * encoder chain.
+ */
+
+/**
+ * DOC:	display driver integration
+ *
  * Display drivers are responsible for linking encoders with the first bridge
  * in the chains. This is done by acquiring the appropriate bridge with
  * devm_drm_of_get_bridge(). Once acquired, the bridge shall be attached to the
···
  * helper to create the &drm_connector, or implement it manually on top of the
  * connector-related operations exposed by the bridge (see the overview
  * documentation of bridge operations for more details).
- *
- * &drm_bridge, like &drm_panel, aren't &drm_mode_object entities like planes,
- * CRTCs, encoders or connectors and hence are not visible to userspace. They
- * just provide additional hooks to get the desired output at the end of the
- * encoder chain.
  */
 
 static DEFINE_MUTEX(bridge_lock);