Did it work with seabios at least ?
For the error, it seems that you're missing dh-autoreconf so :
sudo apt-get install dh-autoreconf
It is also possible to "chainload" the GRUB payload.
So when you boot, it loads "seabios" then instead of searching for HDD or DVD
drive, it loads GRUB payload instead. It is safer this way. (To avoid a
"brick")
https://www.coreboot.org/GRUB2
Roughly, you need to include grub payload into the rom freshly built and also
add a "bootorder" file with this line :
/rom@img/grub2
You can practice with QEMU (Build a rom for i440fx target with seabios only)
to see if it works. The once you're satisfied, you can build again (for your
mobo this time) with seabios and include bootorder file & GRUB payload.
I wish I could recommend Libreboot but the project seems dead. The build
system is broken as well. That's why I recommend using coreboot instead.
