Adding in support for custom configurations

This change will add in the custom _defconfig's to the buildroot
makefile so that when a _defconfig is in the custom directory it is
recognized correctly, and is able to be used.

Makefile

@@ -845,6 +845,10 @@ defconfig: $(BUILD_DIR)/buildroot-config/conf outputmakefile
 	@$(COMMON_CONFIG_ENV) BR2_DEFCONFIG=$(BR2_EXTERNAL)/configs/$@ \
 		$< --defconfig=$(BR2_EXTERNAL)/configs/$@ $(CONFIG_CONFIG_IN)
 
+%_defconfig: $(BUILD_DIR)/buildroot-config/conf $(BR2_EXTERNAL)/custom/configs/%_defconfig outputmakefile
+	@$(COMMON_CONFIG_ENV) BR2_DEFCONFIG=$(BR2_EXTERNAL)/custom/configs/$@ \
+		$< --defconfig=$(BR2_EXTERNAL)/custom/configs/$@ $(CONFIG_CONFIG_IN)
+
 savedefconfig: $(BUILD_DIR)/buildroot-config/conf outputmakefile
 	@$(COMMON_CONFIG_ENV) $< \
 		--savedefconfig=$(if $(DEFCONFIG),$(DEFCONFIG),$(CONFIG_DIR)/defconfig) \
@@ -983,6 +987,12 @@ ifneq ($(wildcard $(BR2_EXTERNAL)/configs/*_defconfig),)
 	@echo 'User-provided configs:'
 	@$(foreach b, $(sort $(notdir $(wildcard $(BR2_EXTERNAL)/configs/*_defconfig))), \
 	  printf "  %-35s - Build for %s\\n" $(b) $(b:_defconfig=);)
+endif
+ifneq ($(wildcard $(BR2_EXTERNAL)/custom/configs/*_defconfig),)
+	@echo
+	@echo 'User-provided custom configs:'
+	@$(foreach b, $(sort $(notdir $(wildcard $(BR2_EXTERNAL)/custom/configs/*_defconfig))), \
+	  printf "  %-35s - Build for %s\\n" $(b) $(b:_defconfig=);)
 endif
 	@echo