cmake: support MCUBoot bootloader natively with SYSBuild

This commit adds CMake and Kconfig files needed to build MCUboot as
an extra image using SYSBuild.

Building an application with MCUBoot using SYSBuild allows users to
build both images using a single build.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>

share/sysbuild/CMakeLists.txt

@@ -37,6 +37,8 @@ ExternalZephyrProject_Add(
   MAIN_APP
 )
 
+add_subdirectory(bootloader)
+
 # This allows for board and app specific images to be included.
 include(${BOARD_DIR}/sysbuild.cmake OPTIONAL)
 include(${APP_DIR}/sysbuild.cmake OPTIONAL)

share/sysbuild/Kconfig

@@ -32,3 +32,5 @@ config WARN_DEPRECATED
 	help
 	  Print a warning when the Kconfig tree is parsed if any deprecated
 	  features are enabled.
+
+rsource "bootloader/Kconfig"

share/sysbuild/bootloader/CMakeLists.txt

@@ -0,0 +1,11 @@
+# Copyright (c) 2022 Nordic Semiconductor
+#
+# SPDX-License-Identifier: Apache-2.0
+
+# Include MCUboot if enabled.
+if(SB_CONFIG_BOOTLOADER_MCUBOOT)
+  ExternalZephyrProject_Add(
+    APPLICATION mcuboot
+    SOURCE_DIR ${ZEPHYR_MCUBOOT_MODULE_DIR}/boot/zephyr/
+  )
+endif()

share/sysbuild/bootloader/Kconfig

@@ -0,0 +1,29 @@
+# Copyright (c) 2022 Nordic Semiconductor
+#
+# SPDX-License-Identifier: Apache-2.0
+
+config SUPPORT_BOOTLOADER
+	bool
+	default y
+
+config SUPPORT_BOOTLOADER_MCUBOOT_ZEPHYR
+	bool
+	default y
+
+choice BOOTLOADER
+	prompt "Bootloader support"
+	default BOOTLOADER_NONE
+	depends on SUPPORT_BOOTLOADER
+
+config BOOTLOADER_NONE
+	bool "None"
+	help
+	  Do not Include a bootloader in the build
+
+config BOOTLOADER_MCUBOOT
+	bool "MCUboot"
+	depends on SUPPORT_BOOTLOADER_MCUBOOT_ZEPHYR
+	help
+	  Include MCUboot (Zephyr port) as the bootloader to use
+
+endchoice