drm/docs: Add todo entry for simple modeset suspend/resume

Add entry for conversion of drivers to new helpers.
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20171106191812.38927-7-noralf@tronnes.org

Documentation/gpu/todo.rst

@@ -185,6 +185,15 @@ are better.
 
 Contact: Sean Paul, Maintainer of the driver you plan to convert
 
+Convert drivers to use simple modeset suspend/resume
+----------------------------------------------------
+
+Most drivers (except i915 and nouveau) that use
+drm_atomic_helper_suspend/resume() can probably be converted to use
+drm_mode_config_helper_suspend/resume().
+
+Contact: Maintainer of the driver you plan to convert
+
 Core refactorings
 =================