esp32: Guard the binary generation with CONFIG_ESP32CORE_BINARY

boards/xtensa/esp32/esp32-core/Kconfig

@@ -38,4 +38,10 @@ config ESP32CORE_RUN_IRAM
 		allows interoperability with the esp-idf system but makes you
 		reliant on the esp-idf design for these parts. Both are possible.
 
+config ESP32CORE_FLASH_IMAGE
+	bool "esp32 flash image"
+	default n
+	---help---
+		Create flash_image.bin mainly used for QEMU.
+
 endif # ARCH_BOARD_ESP32CORE

boards/xtensa/esp32/esp32-core/scripts/Config.mk

@@ -24,6 +24,7 @@
 
 # POSTBUILD -- Perform post build operations
 
+ifeq ($(CONFIG_ESP32CORE_FLASH_IMAGE),y)
 define POSTBUILD
 	@echo "MKIMAGE: ESP32 binary"
         $(Q) if ! esptool.py version ; then \
@@ -47,3 +48,4 @@ define POSTBUILD
 		echo "Generated: flash_image.bin (it can be run with 'qemu-system-xtensa -nographic -machine esp32 -drive file=flash_image.bin,if=mtd,format=raw')"; \
 	fi
 endef
+endif