ARM: EXYNOS: Consolidate Kconfig entries

Instead of repeating the Kconfig entries for every SoC,
move them under ARCH_EXYNOS3, 4 and 5 and move the entries
common to 3, 4 and 5 under ARCH_EXYNOS.

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>