[SeaBIOS] Dealing with fallback and normal coreboot images

[Paul Menzel]

Dear SeaBIOS folks,

coreboot allows to prefix images to add different romstage, ramstage, 
and payloads, and depending on the behavior during boot, choose a 
certain one.

Commonly *normal* and *fallback* are used as prefixes, while the 
bootblock code loads the *normal* image first, but if there is a 
failure, commonly after three tries, boots the fallback image.

SeaBIOS takes runtime configuration values always from `etc/`. That way, 
only one configuration can be used for different coreboot builds.

What could be a solution for that problem? Also allow `fallback/etc/`, 
and `normal/etc`?

Kind regards,

Paul