common: Improve blocksize support for udf

common: Improve blocksize support for udf

Add better support for blocksize selection in _scratch_mkfs_sized
(accept another variant of mkfs options, select correct default block
size if not specified). Also add blocksize selection support to
_scratch_mkfs_blocksized.

For _check_udf_filesystem to keep working when blocksize is not
specified in MKFS_OPTIONS, add detection of blocksize from a mounted
filesystem.

Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>