blk-cgroup: move the cgroup information to struct gendisk

cgroup information only makes sense on a live gendisk that allows
file system I/O (which includes the raw block device).  So move over
the cgroup related members.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Andreas Herrmann <aherrmann@suse.de>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20230203150400.3199230-20-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>