kconfig: move default KBUILD_DEFCONFIG back to scripts/kconfig/Makefile

This is a partial revert of commit 2a86f661 ("kbuild: use
KBUILD_DEFCONFIG as the fallback for DEFCONFIG_LIST").

Now that the reference to $(DEFCONFIG_LIST) was removed from
init/Kconfig, the default KBUILD_DEFCONFIG can go back home.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Makefile

@@ -396,9 +396,6 @@ endif
 KCONFIG_CONFIG	?= .config
 export KCONFIG_CONFIG
 
-# Default file for 'make defconfig'. This may be overridden by arch-Makefile.
-export KBUILD_DEFCONFIG := defconfig
-
 # SHELL used by kbuild
 CONFIG_SHELL := sh
 

scripts/kconfig/Makefile

@@ -9,6 +9,10 @@ else
 Kconfig := Kconfig
 endif
 
+ifndef KBUILD_DEFCONFIG
+KBUILD_DEFCONFIG := defconfig
+endif
+
 ifeq ($(quiet),silent_)
 silent := -s
 endif