With unified builds we may have only a single shared firmware image (bios.bin) in the firmware updater, with a set of root key/vblock fragments, one for each model.

We need a way to create a bios.bin for a particular model. This needs to grab the base bios.bin (e.g. for coral), insert the root key / vblock fragment (e.g. for astronaut) and write the final bios-astronaut.bin file.

This can then then used as a pre-flash image in the factory.

One idea for this is to have a command like:

chromeos-firmwareupdate --generate astronaut