arch/xtensa/esp32: Implement board_boot_image for mcuboot/nxboot support

Documentation/platforms/xtensa/esp32/boards/esp32-devkitc/index.rst

@@ -655,6 +655,12 @@ This configuration is the same as the ``nsh`` configuration, but it generates th
 image in a format that can be used by MCUboot. It also makes the ``make bootloader`` command to
 build the MCUboot bootloader image using the Espressif HAL.
 
+When ``mcuboot`` is used as bootloader, this board uses the
+``board_boot_image()`` implementation in the chain-boot path through
+``boardctl(BOARDIOC_BOOT_IMAGE)``.
+See :doc:`/applications/boot/mcuboot/index` for general MCUboot boot flow
+details and platform requirements.
+
 mcuboot_update_agent
 --------------------
 

boards/xtensa/esp32/common/src/Make.defs

@@ -178,6 +178,10 @@ ifeq ($(CONFIG_ETC_ROMFS),y)
   RCSRCS  = etc/init.d/rc.sysinit etc/init.d/rcS
 endif
 
+ifeq ($(CONFIG_BOARDCTL_BOOT_IMAGE),y)
+  CSRCS += esp32_boot_image.c
+endif
+
 DEPPATH += --dep-path src
 VPATH += :src
 CFLAGS += ${INCDIR_PREFIX}$(TOPDIR)$(DELIM)arch$(DELIM)$(CONFIG_ARCH)$(DELIM)src$(DELIM)board$(DELIM)src