drm/doc: document recommended component helper usage

Now that component has docs it's worth spending a few words and
hyperlinks on recommended best practices in drm.

v2: Add another item that component shouldn't be preferred over
drm_bridge/panel and similar subsystems already providing specialized
support for specific components (Laurent). Also convert to bullet
list.

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Reviewed-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190212164615.13370-1-daniel.vetter@ffwll.ch
diff --git a/Documentation/gpu/drm-internals.rst b/Documentation/gpu/drm-internals.rst
index 3ae23a5..966bd2d 100644
--- a/Documentation/gpu/drm-internals.rst
+++ b/Documentation/gpu/drm-internals.rst
@@ -93,6 +93,11 @@
 Driver Load
 -----------
 
+Component Helper Usage
+~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/gpu/drm/drm_drv.c
+   :doc: component helper usage recommendations
 
 IRQ Helper Library
 ~~~~~~~~~~~~~~~~~~