Adds support for sysbuild loading snippets, these can be included
by using e.g.: cmake ... -DSB_SNIPPET=blah for sysbuild
directly or can be used with an application and sysbuild using
-DSNIPPET. Snippets for sysbuild can use SB_EXTRA_CONF_FILE in the
snippet file to specify an extra Kconfig fragment for sysbuild
Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
Fixes: #73066
Introduce sysbuild_root CMake module similar to the Zephyr root CMake
module. The sysbuild_root CMake module works similar to existing root
module, but with the difference that root paths are adjusted relative to
APP_DIR which is the main image, instead of relative to sysbuild.
Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>
