xen-evtchn.1.0.5 and xen-gnt.1.0.2

Fixes [mirage/mirage#254]

Signed-off-by: David Scott <dave.scott@citrix.com>
Merge pull request #2267 from djs55/mirage-xen

xen-evtchn.1.0.5 and xen-gnt.1.0.2