xen/arm: implement alloc/free_xenballooned_pages with alloc_pages/kfree

Only until we get the balloon driver to work.
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/arm/xen/enlighten.c

@@ -148,3 +148,21 @@ static int __init xen_init_events(void)
 	return 0;
 }
 postcore_initcall(xen_init_events);
+
+/* XXX: only until balloon is properly working */
+int alloc_xenballooned_pages(int nr_pages, struct page **pages, bool highmem)
+{
+	*pages = alloc_pages(highmem ? GFP_HIGHUSER : GFP_KERNEL,
+			get_order(nr_pages));
+	if (*pages == NULL)
+		return -ENOMEM;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(alloc_xenballooned_pages);
+
+void free_xenballooned_pages(int nr_pages, struct page **pages)
+{
+	kfree(*pages);
+	*pages = NULL;
+}
+EXPORT_SYMBOL_GPL(free_xenballooned_pages);