drm/debugfs: show lingering bridges

drm/debugfs: show lingering bridges

The usefulness of /sys/kernel/debug/dri/bridges is limited as it only shows
bridges between drm_bridge_add() and drm_bridge_remove(). However
refcounted bridges can stay allocated and lingering for a long time after
drm_bridge_remove(), and a memory leak due to a missing drm_bridge_put()
would not be visible in this debugfs file.

Add lingering bridges to the /sys/kernel/debug/dri/bridges output.

Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20250915-drm-bridge-debugfs-removed-v9-2-6e5c0aff5de9@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>