Merge branch 'WIP_rauc_fixup' into DEV_jookia

external.mk: Fix rauc-fixups makefile race ...

rauc-fixups would run after buildroot's targets, causing the image to
fail. Instead have it run alongside other world targets.

Revert "rootfs_postbuild: Run rauc_fixups here instead of in the makefile" ...

This solution is actually racy and dirty as it edits stuff outside the
build tree.

This reverts commit 042373f.

Merge branch 'WIP_rauc_fixup' into TMP_jookia

rootfs_postbuild: Run rauc_fixups here instead of in the makefile ...

This ensures the rauc certificates are always fixed up to the latest
config.

Add SPDX-License-Identifier to scripts ...

Clarify the license of copyrighted works made by Xogium.
This deliberately excludes files that may not be copyrightable such as
purely informative files like hashes for packages, config values,
systemd units, and machine generated files.

Reworked certificates handling. The certs.sh.example contains a full example of this, and must be copied to certs.sh, and modified accordingly to reflect the real paths where the certificates are stored. A script that can be called by any board is creating symlinks from the real paths to corresponding statics targets for usage in genimage and postbuild scripts. The certs folder in the external tree must never be distributed in the repository, and is hence ignored via .gitignore.

Initial commit.