drm/fb-helper: Remove drm_fb_helper_connector

All drivers add all their connectors so there's no need to keep around an
array of available connectors. Instead we just put the useable (not
writeback) connectors in a temporary array using
drm_client_for_each_connector_iter() everytime we probe the outputs.
Other places where it's necessary to look at the connectors, we just
iterate over them using the same iterator function.

Rename functions which signature is changed since they will be moved to
drm_client in a later patch.

v6: Improve commit message (Sam Ravnborg)

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190608152657.36613-2-noralf@tronnes.org

Documentation/gpu/todo.rst

@@ -292,6 +292,10 @@ drm_fb_helper tasks
 - The max connector argument for drm_fb_helper_init() and
   drm_fb_helper_fbdev_setup() isn't used anymore and can be removed.
 
+- The helper doesn't keep an array of connectors anymore so these can be
+  removed: drm_fb_helper_single_add_all_connectors(),
+  drm_fb_helper_add_one_connector() and drm_fb_helper_remove_one_connector().
+
 Core refactorings
 =================