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/tree-checker.c

@@ -52,6 +52,7 @@
  * Allows callers to customize the output.
  */
 __printf(4, 5)
+__cold
 static void generic_err(const struct btrfs_fs_info *fs_info,
 			const struct extent_buffer *eb, int slot,
 			const char *fmt, ...)
@@ -76,6 +77,7 @@ static void generic_err(const struct btrfs_fs_info *fs_info,
  * offset has its own meaning.
  */
 __printf(4, 5)
+__cold
 static void file_extent_err(const struct btrfs_fs_info *fs_info,
 			    const struct extent_buffer *eb, int slot,
 			    const char *fmt, ...)
@@ -229,6 +231,7 @@ static int check_csum_item(struct btrfs_fs_info *fs_info,
  * which represents inode number
  */
 __printf(4, 5)
+__cold
 static void dir_item_err(const struct btrfs_fs_info *fs_info,
 			 const struct extent_buffer *eb, int slot,
 			 const char *fmt, ...)