Enable /proc/config.gz and build RPMSG as a module

Without /proc/config.gz booting will stop in pre-switch-root
since /diagnostics.log exists with content.

Also, OMAP remoteproc will try to load the ducati firmware 10 seconds into the boot,
where /system/vendor is not even mounted yet. Build it as a module and let systemd-modules-load handle the rest.