ARM: EXYNOS4: Add support SMDK4412 Board

SMDK4412 board is same as a SMDK4212 board except that
it has EXYNOS4412 SoC, thus it can share machine code
with SMDK4212.

This patch renames mach-smdk4212.c to mach-smdk4x12.c
to support both SMDK4212 and SMDK4412 board with one
machine file.

Signed-off-by: Changhwan Youn <chaos.youn@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>