TFTP_IP support for older Pis with bootcode.bin on SD card

[gbaman]

Describe the bug The Pi 4 includes the ability to set a TFTP_IP value in the EEPROM, a very useful feature when the network boot server has a known fixed IP address. For older Pis that use an updated network bootloader on an SD card via bootcode.bin (and nothing else), there doesn't seem to be any way to do this?

Expected behaviour A method for specifying a fixed IP on the SD card for the tftp server, assuming via the config.txt file?

Actual behaviour There doesn't seem to be a way to specify a fixed tftp server IP address on the SD card of older Pis, only on Pi 4.

Additional context Having this fixed IP option would allow organisations using older Pis to guarantee the Pi will always boot from a fixed IP address, no matter what else is going on on the network. There are still plenty of older Pis out there in use and it would certainly simplify our processes with a batch of Pi 3B+s, where we already put the bootcode.bin on each SD card.