losetup: Add support for logical block size

losetup: Add support for logical block size

Kernel since 4.14 supports setting of logical block size[1]. It allows to
create loop devices that report logical block size different from 512.

Add support for this feature to losetup.

References:
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/block/loop.c?id=89e4fdecb51cf5535867026274bc97de9480ade5

[kzak@redhat.com: - fix loopcxt_get_blocksize()
                  - remove lo_blocksize from loop_info64]

Signed-off-by: Stanislav Brabec <sbrabec@suse.cz>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Karel Zak <kzak@redhat.com>