Our initramfs images are supposed to be small and don't have a
/etc/opkg folder so attempting to put feed config in there will
fail. Reset the FEED_URIS that come from our local.conf.
The partition layout needed for rauc is different from the one created
by the existing installer (based on the live image).
An initramfs-framework module for installation to the sysmocom-idu is
added. It is included in a corresponding initramfs image for use on an
USB memory stick.