Flash Region 1 (BIOS): 00400000 - 00ffffff Flash Region 8 (EC): 07fff000 - 00000fff (unused)
Looking at the contents of flash.bin then the EC firmware is located at offset 0x400000 which would appear to put it at the start of the IFD BIOS partition.
Yep, the EC firmware is at the beginning of the BIOS partition then, which isn't too unusual. Some of the first bytes of the flash within the IFD section are likely some sort of pointer or jump to the beginning of the EC firmware; sometimes the pointer case it's not an offset in bytes, but in 256 or 4096 bytes. There might also be some sort of magic bytes or checksum in the first few bytes so that the EC can detect if the flash probably contains a valid firmware image for the EC, so it doesn't just load random bytes when the flash doesn't contain the EC firmware.
Looks like the example of the mandolin board is going to be the one to follow.
You probably want to take the x210's fmd file as a starting point though, since that one is for an Intel system and leaves space for the IFD/ME/GBE partition; you'll probably need to adjust the sizes and offsets. The Makefile part is a bit clearer on the Mandolin board, but it does basically the same as the x210's EC driver.