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>
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index e0d8565..faa36d7 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1232,6 +1232,8 @@
 	 */
 	if (mdesc->map_io)
 		mdesc->map_io();
+	else
+		debug_ll_io_init();
 	fill_pmd_gaps();
 
 	/* Reserve fixed i/o space in VMALLOC region */