Tested on AMT host with working comconsole_pcidev setting and host with physical RS-232 com port:
```
console="comconsole"
comconsole_speed="115200"
comconsole_pcidev="0:22:3"
```
No change to working AMT host.
Real serial no longer explodes in BTX and emits useable errors:
```
Consoles: serial port
BIOS drive C: is disk0
PXE version 2.1, real mode entry point @98d1:0106
BIOS 632kB/3134016kB available memory
FreeBSD/x86 bootstrap loader, Revision 1.1
(Sat Dec 16 11:20:40 MST 2017 sbruno@lab)
Loading /boot/defaults/loader.conf
Cannot find specified pcidev
Warning: bad definition on file /boot/loader.conf
comconsole_pcidev="0:22:3"
```