drm/todo: Add entry to clean up former seltests suites

Most of those suites are undocumented and aren't really clear about what
they are testing. Let's add a TODO entry as a future task to get started
into KUnit and DRM.
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Link: https://lore.kernel.org/r/20231025132428.723672-2-mripard@kernel.orgSigned-off-by: Maxime Ripard <mripard@kernel.org>

Documentation/gpu/todo.rst

@@ -621,6 +621,23 @@ Contact: Javier Martinez Canillas <javierm@redhat.com>
 
 Level: Intermediate
 
+Clean up and document former selftests suites
+---------------------------------------------
+
+Some KUnit test suites (drm_buddy, drm_cmdline_parser, drm_damage_helper,
+drm_format, drm_framebuffer, drm_dp_mst_helper, drm_mm, drm_plane_helper and
+drm_rect) are former selftests suites that have been converted over when KUnit
+was first introduced.
+
+These suites were fairly undocumented, and with different goals than what unit
+tests can be. Trying to identify what each test in these suites actually test
+for, whether that makes sense for a unit test, and either remove it if it
+doesn't or document it if it does would be of great help.
+
+Contact: Maxime Ripard <mripard@kernel.org>
+
+Level: Intermediate
+
 Enable trinity for DRM
 ----------------------