btrfs: prepare zlib to support bs > ps cases

This involves converting the following functions to use correct folio
sizes/shifts:

- zlib_compress_folios()
- zlib_decompress_bio()

There is a special handling for s390 hardware acceleration.
With bs > ps cases, we can go with 16K block size on s390 (which uses
fixed 4K page size).
In that case we do not need to do the buffer copy as our folio is large
enough for hardware acceleration.

So factor out the s390 specific and folio size check into a helper,
need_special_buffer().

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>