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.
Now that the uncut FIT is stored in primary/secondary, we don't create
any FIT header files.
Fixes: 499a8f7 ("common: Create (e)MMC image with redundant root filesystems")
This image contains:
- A partition to hold bootloader config ("aux").
- Two redundant copies of the FIT framed rootfs (which will be
upgradable by RAUC from within Infix).
- A partition to store critical configuration data ("cfg")
- A partition to store data created dynamically by Infix ("var")