btrfs: add more __cold annotations

The __cold functions are placed to a special section, as they're
expected to be called rarely. This could help i-cache prefetches or help
compiler to decide which branches are more/less likely to be taken
without any other annotations needed.

Though we can't add more __exit annotations, it's still possible to add
__cold (that's also added with __exit). That way the following function
categories are tagged:

- printf wrappers, error messages
- exit helpers

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

fs/btrfs/delayed-inode.h

@@ -149,7 +149,7 @@ int btrfs_readdir_delayed_dir_index(struct dir_context *ctx,
 
 /* for init */
 int __init btrfs_delayed_inode_init(void);
-void btrfs_delayed_inode_exit(void);
+void __cold btrfs_delayed_inode_exit(void);
 
 /* for debugging */
 void btrfs_assert_delayed_root_empty(struct btrfs_fs_info *fs_info);