drm/bridge: adapt drm_bridge_add/remove() docs, mention the lingering list

drm/bridge: adapt drm_bridge_add/remove() docs, mention the lingering list

The role of drm_bridge_add/remove() is more complex now after having added
the lingering list. Update the kdoc accordingly.

Also stop mentioning the global list(s) in the first line of the docs: the
most important thing to mention here is that bridges are registered and
deregistered, lists are just the type of container used to implement such
(de)registration.

Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20250915-drm-bridge-debugfs-removed-v9-3-6e5c0aff5de9@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>