drm/todo: add entry about converting to of_drm_find_and_get_bridge()

drm/todo: add entry about converting to of_drm_find_and_get_bridge()

of_drm_find_bridge() is deprecated, but converting some users is very
complex and should be reasonably doable only after the DRM panel bridge
lifetime rework. Add a TODO to track this.

Suggested-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/dri-devel/20250319-stylish-lime-mongoose-0a18ad@houat/
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patch.msgid.link/20251216-drm-bridge-alloc-getput-drm_of_find_bridge-v3-3-b5165fab8058@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>