orion5x: kconfig: move board select menu and common settings

Becuase the board select menu in arch/arm/Kconfig is too big,
move the Orion5x board select menu to orion5x/Kconfig.

Move also common settings (CONFIG_SYS_CPU="arm926ejs" and
CONFIG_SYS_SOC="orion5x").

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
diff --git a/configs/edminiv2_defconfig b/configs/edminiv2_defconfig
index 82aa684..3b1a6c1 100644
--- a/configs/edminiv2_defconfig
+++ b/configs/edminiv2_defconfig
@@ -1,2 +1,3 @@
 CONFIG_ARM=y
+CONFIG_ORION5X=y
 CONFIG_TARGET_EDMINIV2=y