xen: use generic functions instead of xen_{alloc, free}_vm_area()

Replace calls to the Xen-specific xen_alloc_vm_area() and
xen_free_vm_area() functions with the generic equivalent
(alloc_vm_area() and free_vm_area()).

On x86, these were identical already.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c
index cdacf92..229d3ad 100644
--- a/drivers/xen/xenbus/xenbus_client.c
+++ b/drivers/xen/xenbus/xenbus_client.c
@@ -443,7 +443,7 @@
 
 	*vaddr = NULL;
 
-	area = xen_alloc_vm_area(PAGE_SIZE);
+	area = alloc_vm_area(PAGE_SIZE);
 	if (!area)
 		return -ENOMEM;
 
@@ -453,7 +453,7 @@
 		BUG();
 
 	if (op.status != GNTST_okay) {
-		xen_free_vm_area(area);
+		free_vm_area(area);
 		xenbus_dev_fatal(dev, op.status,
 				 "mapping in shared page %d from domain %d",
 				 gnt_ref, dev->otherend_id);
@@ -552,7 +552,7 @@
 		BUG();
 
 	if (op.status == GNTST_okay)
-		xen_free_vm_area(area);
+		free_vm_area(area);
 	else
 		xenbus_dev_error(dev, op.status,
 				 "unmapping page at handle %d error %d",