MAINTAINERS: add git repository for Xen
MAINTAINERS: add git repository for Xen

Signed-off-by: David Vrabel <b9d45bd1f671e508cd8daa63dfc3cabb597562df@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <da3a51b335cef0eb0e2c329c5ef6bcd6acef687a@oracle.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs