ARM: EXYNOS: Consolidate exynos4 and exynos5 machine files

Since there is very little difference between these two files,
they can be easily combined into one with necessary SoC checks.
While at it also merge the common.c file into this as it does
not have any other users.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>