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>