dm zoned: convert to xarray

The zones array is getting really large, and large arrays tend to
wreak havoc with the CPU caches.  So convert it to xarray to become
more cache friendly.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com> # fix leak in dmz_insert
Signed-off-by: Mike Snitzer <snitzer@redhat.com>