xen: move Xen-testing predicates to common header

Move xen_domain and related tests out of asm-x86 to xen/xen.h so they
can be included whenever they are necessary.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
diff --git a/drivers/xen/sys-hypervisor.c b/drivers/xen/sys-hypervisor.c
index 88a60e0..ae5cb05 100644
--- a/drivers/xen/sys-hypervisor.c
+++ b/drivers/xen/sys-hypervisor.c
@@ -14,6 +14,7 @@
 #include <asm/xen/hypervisor.h>
 #include <asm/xen/hypercall.h>
 
+#include <xen/xen.h>
 #include <xen/xenbus.h>
 #include <xen/interface/xen.h>
 #include <xen/interface/version.h>