Meanwhile... I found we can add uart on pci in bhyve (and get /dev/term/0 in os) - it is not getting driver in UEFI firmware, but for purposes of implementing OS console support to use such combination, the firmware/bootloader phase does not matter much (except eventually we want to get port naming right).

kind of annoying fact is that bhyve is creating ports a-d too, even if only a has defined backend and firmware is thinking we have ports a and b:)