drm/docs: Discourage adding more to kms-properties.csv

Motivated by patch review.

The table is really hard to read in source form, hard to edit, and
we've moved away to more focused sections about specific features and
how they're exposed in properties.

Those sections can then more easily enumerate options, link to helper
functions and other parts of the docs. All things that get ugly real
fast in the docs.

Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180219225356.24996-1-daniel.vetter@ffwll.ch

Documentation/gpu/drm-kms.rst

@@ -547,8 +547,9 @@ Explicit Fencing Properties
 Existing KMS Properties
 -----------------------
 
-The following table gives description of drm properties exposed by
-various modules/drivers.
+The following table gives description of drm properties exposed by various
+modules/drivers. Because this table is very unwieldy, do not add any new
+properties here. Instead document them in a section above.
 
 .. csv-table::
    :header-rows: 1