Xen: depend on xen-evtchn and xen-gnt rather than xen-event and xen-grant

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #86 from djs55/remove-xenctrl

Xen: depend on xen-evtchn and xen-gnt rather than xen-event and xen-gran...