xen/balloon: make alloc_xenballoon_pages() always allocate low pages

All users of alloc_xenballoon_pages() wanted low memory pages, so
remove the option for high memory.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
diff --git a/include/xen/balloon.h b/include/xen/balloon.h
index c8aee7a..83efdeb 100644
--- a/include/xen/balloon.h
+++ b/include/xen/balloon.h
@@ -22,8 +22,7 @@
 
 void balloon_set_new_target(unsigned long target);
 
-int alloc_xenballooned_pages(int nr_pages, struct page **pages,
-		bool highmem);
+int alloc_xenballooned_pages(int nr_pages, struct page **pages);
 void free_xenballooned_pages(int nr_pages, struct page **pages);
 
 struct device;