block: move the bdi from the request_queue to the gendisk

The backing device information only makes sense for file system I/O,
and thus belongs into the gendisk and not the lower level request_queue
structure.  Move it there.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20210809141744.1203023-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/genhd.h

@@ -158,6 +158,7 @@ struct gendisk {
 	struct mutex open_mutex;	/* open/close mutex */
 	unsigned open_partitions;	/* number of open partitions */
 
+	struct backing_dev_info	*bdi;
 	struct kobject *slave_dir;
 #ifdef CONFIG_BLOCK_HOLDER_DEPRECATED
 	struct list_head slave_bdevs;