This is the layout expected by the "distro boot" effort in U-Boot.
As far as I understand, the contract is:
- U-Boot built for `fooboard` by `vendor`, will set the `fdtfile`
variable to `vendor/fooboard.dtb` - or more precisely: matching
whatever path the dtb is built at in the kernel tree.
- A distro (e.g. Infix) then just needs to specify the `fdtdir` in its
syslinux config (/boot in our case), and U-Boot will be able to find
the correct dtb.
Store FIT headers separately on aux, and place the raw SquashFS images
on primary/secondary. This removes the need to muck about with the
device mapper to setup the rootfs, and it allows us to boot using
syslinux files.
