xen: export ioctl headers to userspace

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

include/Kbuild

@@ -8,3 +8,4 @@ header-y += mtd/
 header-y += rdma/
 header-y += video/
 header-y += drm/
+header-y += xen/

include/xen/Kbuild

@@ -0,0 +1 @@
+header-y += evtchn.h