Hi
Either one of these should be portable to the Coldfire architecture, but I suspect that yaffs would be easier, simply because it is less closely linked to Linux and more ports have been made already.
Have you considered the licensing implications? Both of these are GPL'd so your bare metal application will also have to be GPL because of the viral nature of GPL. There are other alternative licenses for yaffs, but you'd need to check with Aleph1 (
http://www.aleph1.co.uk/node/33).
If you can't use GPL source or can't afford Aleph1's license fees, then you may want to consider writing a less ambitious filing system yourself. A full blown journalling filing system may be overkill for an application that doesn't require an OS.
Cheers,
Paul.