drm/todo: Add entry for converting kselftests to kunit

Many of the kselftests in DRM can be converted to kunit tests instead,
since that framework is more suitable for unit testing.
Suggested-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220509130846.694397-1-javierm@redhat.com

Documentation/gpu/todo.rst

@@ -617,6 +617,17 @@ Contact: Javier Martinez Canillas <javierm@redhat.com>
 
 Level: Intermediate
 
+Convert Kernel Selftests (kselftest) to KUnit tests when appropriate
+--------------------------------------------------------------------
+
+Many of the `Kselftest <https://www.kernel.org/doc/html/latest/dev-tools/kselftest.html>`_
+tests in DRM could be converted to Kunit tests instead, since that framework
+is more suitable for unit testing.
+
+Contact: Javier Martinez Canillas <javierm@redhat.com>
+
+Level: Starter
+
 Enable trinity for DRM
 ----------------------