drm/panthor: enable fdinfo for memory stats

Implement drm object's status callback.

Also, we consider a PRIME imported BO to be resident if its matching
dma_buf has an open attachment, which means its backing storage had already
been allocated.

Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240923230912.2207320-5-adrian.larumbe@collabora.com