btrfs: factor out sysfs code for updating sprout fsid

Wrap the fsid renaming code and move it to sysfs.c.

Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/sysfs.h

@@ -87,6 +87,8 @@ int btrfs_sysfs_add_fsid(struct btrfs_fs_devices *fs_devs,
 				struct kobject *parent);
 int btrfs_sysfs_add_device(struct btrfs_fs_devices *fs_devs);
 void btrfs_sysfs_remove_fsid(struct btrfs_fs_devices *fs_devs);
+void btrfs_sysfs_update_sprout_fsid(struct btrfs_fs_devices *fs_devices,
+				    const u8 *fsid);
 void btrfs_sysfs_feature_update(struct btrfs_fs_info *fs_info,
 		u64 bit, enum btrfs_feature_set set);
 void btrfs_kobject_uevent(struct block_device *bdev, enum kobject_action action);