ARM: SAMSUNG: fix to support for missing cpu specific map_io

Since commit 7ed76e08 (ARM: EXYNOS: Fix low level debug support)
map_io() is not needed for exynos5440 so need to fix to lookup
cpu which using map_io(). Without this, kernel boot log complains
'CPU EXYNOS5440 support not enabled' on exynos5440 and panic().
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>

arch/arm/plat-samsung/init.c

@@ -55,12 +55,13 @@ void __init s3c_init_cpu(unsigned long idcode,
 
 	printk("CPU %s (id 0x%08lx)\n", cpu->name, idcode);
 
-	if (cpu->map_io == NULL || cpu->init == NULL) {
+	if (cpu->init == NULL) {
 		printk(KERN_ERR "CPU %s support not enabled\n", cpu->name);
 		panic("Unsupported Samsung CPU");
 	}
 
-	cpu->map_io();
+	if (cpu->map_io)
+		cpu->map_io();
 }
 
 /* s3c24xx_init_clocks