block: move rescan_partitions to fs/block_dev.c

Large parts of rescan_partitions aren't about partitions, and
moving it to block_dev.c will allow for some further cleanups by
merging it into its only caller.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index fd7774e..f5cffbf 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -621,9 +621,9 @@ extern void blk_invalidate_devt(dev_t devt);
 extern dev_t blk_lookup_devt(const char *name, int partno);
 extern char *disk_name (struct gendisk *hd, int partno, char *buf);
 
+int blk_add_partitions(struct gendisk *disk, struct block_device *bdev);
+int blk_drop_partitions(struct gendisk *disk, struct block_device *bdev);
 extern int disk_expand_part_tbl(struct gendisk *disk, int target);
-int rescan_partitions(struct gendisk *disk, struct block_device *bdev,
-		bool invalidate);
 extern struct hd_struct * __must_check add_partition(struct gendisk *disk,
 						     int partno, sector_t start,
 						     sector_t len, int flags,