MAINTAINERS: Add in two extra co-maintainers of the Xen tree.

Both Boris and David have graciously volunteered to help in
maintaining the Xen subsystem tree. Cementing this in the
MAINTAINERS file so they are copied on Xen related patches.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: David Vrabel <david.vrabel@citrix.com>

MAINTAINERS

@@ -9238,6 +9238,8 @@ F:	drivers/media/tuners/tuner-xc2028.*
 XEN HYPERVISOR INTERFACE
 M:	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
 M:	Jeremy Fitzhardinge <jeremy@goop.org>
+M:	Boris Ostrovsky <boris.ostrovsky@oracle.com>
+M:	David Vrabel <david.vrabel@citrix.com>
 L:	xen-devel@lists.xenproject.org (moderated for non-subscribers)
 S:	Supported
 F:	arch/x86/xen/