nomadik: kconfig: move board select menu and common settings

Becuase the board select menu in arch/arm/Kconfig is too big,
move the Nomadik board select menu to nomadik/Kconfig.

Move also common settings (CONFIG_SYS_CPU="arm926ejs" and
CONFIG_SYS_SOC="nomadik").

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/configs/nhk8815_defconfig b/configs/nhk8815_defconfig
index 3d20199..f661226 100644
--- a/configs/nhk8815_defconfig
+++ b/configs/nhk8815_defconfig
@@ -1,2 +1,3 @@
 CONFIG_ARM=y
-CONFIG_TARGET_NHK8815=y
+CONFIG_ARCH_NOMADIK=y
+CONFIG_NOMADIK_NHK8815=y