loader.conf(5) documents comconsole and comconsole_speed, but not comconsole_port or comconsole_pcidev
The docs for all four variables are in loader(8).
I'm told maintaining the same info in multiple places is wrong. Probably should all be in loader.conf(5) and let loader(8) refer there. Or vica versa. Don't care, so long as it's a consistent place and the reader is told where to look.