Becuase the board select menu in arch/arm/Kconfig is too big,
move the Exynos board select menu to exynos/Kconfig.
Consolidate also common settings (CONFIG_SYS_CPU="armv7" and
CONFIG_SYS_SOC="exynos").
Signed-off-by: Masahiro Yamada
Acked-by: Minkyu Kang