kbuild: remove scripts/multiconfig.sh

We have switched to the single .config configuration system,
the same one as used in Linux Kernel.

The necessary glue code is small enough now, so move it to the
top-level Makefile and scripts/kconfig/Makefile, and then delete
scripts/multiconfig.sh.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

scripts/kconfig/Makefile

@@ -5,6 +5,12 @@
 PHONY += oldconfig xconfig gconfig menuconfig config silentoldconfig update-po-config \
 	localmodconfig localyesconfig
 
+# Added for U-Boot
+#  Linux has defconfig files in arch/$(SRCARCH)/configs/,
+#  on the other hand, U-Boot does in configs/.
+#  Set SRCARCH to .. fake this Makefile.
+SRCARCH := ..
+
 ifdef KBUILD_KCONFIG
 Kconfig := $(KBUILD_KCONFIG)
 else
@@ -104,6 +110,10 @@ endif
 %_defconfig: $(obj)/conf
 	$(Q)$< --defconfig=arch/$(SRCARCH)/configs/$@ $(Kconfig)
 
+# Added for U-Boot (backward compatibility)
+%_config: %_defconfig
+	@:
+
 configfiles=$(wildcard $(srctree)/kernel/configs/$(1).config $(srctree)/arch/$(SRCARCH)/configs/$(1).config)
 
 define mergeconfig