ARM: EXYNOS: fix CONFIG_DEBUG_LL

addruart cannot read from the physical address of the chipid
register, that will fail as soon as the mmu is turned on.
Fixing it to read from the physical or virtual address depending
on the mmu state also does not work, because there is a period
between head.S and exynos_map_io where the mmu is on, the uart
is mapped and used, but the chipid mapping is not yet present.

Fix addruart to use the ARM Main ID cp15 register to determine
if the core is Cortex A15 (EXYNOS5) or not (EXYNOS4).

Signed-off-by: Colin Cross <ccross@android.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Thomas Abraham <thomas.abraham@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>