tests: Document OVMF setup
For context, see:
Linus:
It seems like we're looking for a file in a couple of possible directories.
I think it'd be a little more obvious, when reading it, if we listed the alternatives in preferred order and broke out of the loop as soon as we succeed ("break"). Slightly more efficient too, but that's not the point.
Rasmus:
Added comment that this is currently "magic" from st/core/st repo. How about I open an issue once this is closed, paging one of our firmware experts to explain+document? I didn't dig, just seemed like copying firmware vars and stuff so that qemu had something to use.
Linus:
Sounds good.
Paging @kai @zaolin, can either of you fix this? Please assign yourself if so.