xen: Add export.h for THIS_MODULE/EXPORT_SYMBOL to various xen users.

Things like THIS_MODULE and EXPORT_SYMBOL were simply everywhere
because module.h was also everywhere.  But we are fixing the latter.
So we need to call out the real users in advance.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c
index cdacf92..b63540d 100644
--- a/drivers/xen/xenbus/xenbus_client.c
+++ b/drivers/xen/xenbus/xenbus_client.c
@@ -33,6 +33,7 @@
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/vmalloc.h>
+#include <linux/export.h>
 #include <asm/xen/hypervisor.h>
 #include <xen/interface/xen.h>
 #include <xen/interface/event_channel.h>