kbuild: Add config fragment merge functionality

So far this function was only used locally in powerpc, some other
architectures might benefit from it. Move it into
scripts/Makefile.defconf.
Signed-off-by: NNicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: NAlexander Stein <alexander.stein@ew.tq-group.com>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230124110213.3221264-10-alexander.stein@ew.tq-group.comSigned-off-by: NArnd Bergmann <arnd@arndb.de>

arch/powerpc/Makefile

@@ -253,17 +253,7 @@ PHONY += bootwrapper_install
 bootwrapper_install:
 	$(Q)$(MAKE) $(build)=$(boot) $(patsubst %,$(boot)/%,$@)
 
-# Used to create 'merged defconfigs'
-# To use it $(call) it with the first argument as the base defconfig
-# and the second argument as a space separated list of .config files to merge,
-# without the .config suffix.
-define merge_into_defconfig
-	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/kconfig/merge_config.sh \
-		-m -O $(objtree) $(srctree)/arch/$(ARCH)/configs/$(1) \
-		$(foreach config,$(2),$(srctree)/arch/$(ARCH)/configs/$(config).config)
-	+$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig
-endef
-
+include $(srctree)/scripts/Makefile.defconf
 PHONY += pseries_le_defconfig
 pseries_le_defconfig:
 	$(call merge_into_defconfig,pseries_defconfig,le)

scripts/Makefile.defconf

+# SPDX-License-Identifier: GPL-2.0
+# Configuration heplers
+
+# Creates 'merged defconfigs'
+# ---------------------------------------------------------------------------
+# Usage:
+#   $(call merge_into_defconfig,base_config,config_fragment1 config_fragment2 ...)
+#
+# Input config fragments without '.config' suffix
+define merge_into_defconfig
+	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/kconfig/merge_config.sh \
+		-m -O $(objtree) $(srctree)/arch/$(ARCH)/configs/$(1) \
+		$(foreach config,$(2),$(srctree)/arch/$(ARCH)/configs/$(config).config)
+	+$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig
+endef