drm/panthor: Add an ioctl to query BO flags

drm/panthor: Add an ioctl to query BO flags

This is useful when importing BOs, so we can know about cacheability
and flush the caches when needed.

We can also know when the buffer comes from a different subsystem and
take proper actions (avoid CPU mappings, or do kernel-based syncs
instead of userland cache flushes).

v2:
- New commit

v3:
- Add Steve's R-b

v4:
- No changes

v5:
- No changes

v6:
- No changes

v7:
- No changes

v8:
- No changes

Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://patch.msgid.link/20251208100841.730527-6-boris.brezillon@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>