xen: re-enable boot-time ballooning

Now that the balloon driver doesn't stumble over non-RAM pages, we
can enable the extra space for ballooning.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 769c4b0..630fb53 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -248,8 +248,7 @@
 	else
 		extra_pages = 0;
 
-	if (!xen_initial_domain())
-		xen_add_extra_mem(extra_pages);
+	xen_add_extra_mem(extra_pages);
 
 	return "Xen";
 }