Provide images for fwupd

[varac]

Coreboot Support Is Being Worked On For Fwupd/LVFS

It would be awesome to have signed images available for even easier updating (after initial hardware flashing of course) ! There's [already the first vendor which provides (unsigned) images](https://fwupd.org/lvfs/search?value=coreboot]. What do you think ?

[merge]

afaik you still need the vendor's signature for these images. Anyways it doesn't seem to be as straight forward as could be for us.

[boniek83]

This would perfectly complement overall spirit of the project - easy coreboot.