drm/panfrost: show device-wide list of DRM GEM objects over DebugFS

This change is essentially a Panfrost port of commit a3707f53
("drm/panthor: show device-wide list of DRM GEM objects over DebugFS").

The DebugFS file is almost the same as in Panthor, minus the GEM object
usage flags, since Panfrost has no kernel-only BO's.

Two additional GEM state flags which are displayed but aren't relevant
to Panthor are 'Purged' and 'Purgeable', since Panfrost implements an
explicit shrinker and a madvise ioctl to flag objects as reclaimable.

Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://lore.kernel.org/r/20250520174634.353267-5-adrian.larumbe@collabora.com