ARM: mmu: Call debug_ll_io_init if no map_io function is specified

More and more sub-architectures are using only the debug_ll_io_init
function as the map_io function. Make the core code call this function
if no function is specified in the machine description to remove some
boilerplate code.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/mm/mmu.c

@@ -1232,6 +1232,8 @@ static void __init devicemaps_init(struct machine_desc *mdesc)
 	 */
 	if (mdesc->map_io)
 		mdesc->map_io();
+	else
+		debug_ll_io_init();
 	fill_pmd_gaps();
 
 	/* Reserve fixed i/o space in VMALLOC region */