xen: disable all non-virtual drivers

A domU Xen environment has no non-virtual drivers, so make sure
they're all disabled at once.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>

arch/i386/xen/setup.c

@@ -91,4 +91,6 @@ void __init xen_arch_setup(void)
 	/* fill cpus_possible with all available cpus */
 	xen_fill_possible_map();
 #endif
+
+	paravirt_disable_iospace();
 }