exynos: kconfig: move board select menu and common settings

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 <yamada.m@jp.panasonic.com>
Acked-by: Minkyu Kang <mk7.kang@samsung.com>
diff --git a/configs/s5pc210_universal_defconfig b/configs/s5pc210_universal_defconfig
index 572df1d..a9a3446 100644
--- a/configs/s5pc210_universal_defconfig
+++ b/configs/s5pc210_universal_defconfig
@@ -1,2 +1,3 @@
 CONFIG_ARM=y
+CONFIG_ARCH_EXYNOS=y
 CONFIG_TARGET_S5PC210_UNIVERSAL=y