mkimage will generate an FIT image containing a signature of the
rootfs, where the data is kept out of the DTB data structure, i.e.:
.---------.
| DTB |
:---------:
| Padding |
:---------:
| |
| |
| rootfs |
| |
| |
'---------'
This is the on-disk format of Infix. At boot, we extract kernel and
device trees from the rootfs, and then use Linux's device mapper to
create a virtual block device that exposes the rootfs (squash).
