update to v3.4.0 / use a released tag from upstream
no downstream change. just use a "stable" upstream base. It fixed a Kconfig issue I have with our current base.
@angus.ainslie This is just a first step before I can fix the build and packaging without west. I'm not even sure whether I must wait for your Ack in this case but I'll do so, just to see whether you are ok with a merge like this.