[coreboot] POST cards, I/O ports and M.2 to MiniPCIe

[Trammell Hudson]

How soon after reset are port 0x80 messages available on a MiniPCIe
attached POST card?  And would the POST card be expected to work with
a M.2 to MiniPCIe adapter?  How is the ISA bus' I/O address space mapped
to PCIe devices?

I'm dealing an early bring-up problem on a modern architecture without
serial ports and wondering if that would a good way to debug it.