sunxi: kconfig: Add top-level ARCH_SUNXI

And make TARGET_SUN[45678]I a choice variable under this.

configs updated with:
    sed -i -e 's/^\(\+S:\)\?CONFIG_TARGET_SUN.I=y/\1CONFIG_ARCH_SUNXI=y\n&/g' configs/*

Signed-off-by: Ian Campbell <ijc@hellion.org.uk>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
diff --git a/configs/Mini-X_defconfig b/configs/Mini-X_defconfig
index 6718dcb..adccb8b 100644
--- a/configs/Mini-X_defconfig
+++ b/configs/Mini-X_defconfig
@@ -2,4 +2,5 @@
 CONFIG_SYS_EXTRA_OPTIONS="MINI_X,AXP209_POWER,USB_EHCI"
 CONFIG_FDTFILE="sun4i-a10-mini-xplus.dtb"
 +S:CONFIG_ARM=y
++S:CONFIG_ARCH_SUNXI=y
 +S:CONFIG_TARGET_SUN4I=y