- Adapt boot scripts to exepect the split FIT header/SquashFS image
layout.
- Make sure that we can boot from any kind of block device (most
importantly virtio for GNS3).
- Rename net -> dhcp as we might have more kinds of netboots in the
future (http).
Ensure that whenever U-Boot is built:
- The chosen signing key and is converted to the expected format and
installed in the build tree.
- Infix's environment extensions are installed in the build tree