[yocto] Building multiple U-Boot configurations

[colin.helliwell at ln-systems.com]

Just wondering if there's a clean n simple way to modify machine/recipe
configs such that I can build two versions of U-Boot - one for development,
one for production. 
Obviously I'll need to watch out for which one is 'deployed', but unsure of
a nice way to get two built - separate recipes which pull in the different
configs/patches? 
Any gotchas I'd need to be aware of when it comes to the interaction with
the rest of the image generation; or would it just be safer to take the
approach of having separate images? (That wouldn't be so usable, since it'll
only be u-boot that's different between the two - I'd prefer to get both
generated from a single bitbake)