Kconfig: introduce ARCH_DEFCONFIG to DEFCONFIG_LIST

init/Kconfig contains a list of configs that are searched
for if 'make *config' are used with no .config present.
Extend this list to look at the config identified by
ARCH_DEFCONFIG.

With this change we now try the defconfig targets last.

This fixes a regression reported
by: Linus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
diff --git a/init/Kconfig b/init/Kconfig
index 6135d07..6199d11 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -13,6 +13,7 @@
 	default "/lib/modules/$UNAME_RELEASE/.config"
 	default "/etc/kernel-config"
 	default "/boot/config-$UNAME_RELEASE"
+	default "$ARCH_DEFCONFIG"
 	default "arch/$ARCH/defconfig"
 
 menu "General setup"