drm/todo: Add some cleanup tasks

Motivated by review comments from Ville&Sean.

Cc: Ville Syrjälä <[e-mail]>
Cc: Sean Paul <[e-mail]>
Reviewed-by: Ville Syrjälä <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

Documentation/gpu/todo.rst

···
   leftovers from older (never merged into upstream) KMS designs where modes
   where set using their ID, including support to add/remove modes.
 
+- Make ->funcs and ->helper_private vtables optional. There's a bunch of empty
+  function tables in drivers, but before we can remove them we need to make sure
+  that all the users in helpers and drivers do correctly check for a NULL
+  vtable.
+
+- Cleanup up the various ->destroy callbacks. A lot of them just wrapt the
+  drm_*_cleanup implementations and can be removed. Some tack a kfree() at the
+  end, for which we could add drm_*_cleanup_kfree(). And then there's the (for
+  historical reasons) misnamed drm_primary_helper_destroy() function.
+
 Better Testing
 ==============