This dependency is required for adequate Parallels images support.
Typically the disk consists of several images which are glued by
XML disk descriptor. Also XML hides inside several important parameters
which are not available in the image header.

The patch also adds clause to checkpatch.pl to understand libxml2 types.
Signed-off-by: NDenis V. Lunev <den@openvz.org>
Signed-off-by: NKlim Kireev <klim.kireev@virtuozzo.com>
Signed-off-by: NEdgar Kaziakhmedov <edgar.kaziakhmedov@virtuozzo.com>
Signed-off-by: NVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-id: 20180112090122.1702-3-klim.kireev@virtuozzo.com
CC: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>