Export compress_pages, decompress_bio and decompress callbacks for all
compression algos. The indirect calls will be replaced by a switch.
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>