Hi Andrea,
Is this actually a PC? A little Googling makes me think it's a gaming machine which may explain the "igt_secure" payload, in which case it may be designed to phone home or do some validation before booting the OS.
I think Paul has the right idea - see if it will boot from USB or whatever other media is available. If you can flash the firmware image then you can try swapping the payload with something else; the 16MB ROM should even be big enough to fit a minimal Linux kernel if you don't have ports for USB, SATA, etc. in that device.
The CPU is a Haswell which is still fairly popular in coreboot. If you have detailed hardware information then you might try to add a new mainboard target for your system. There are several examples in the src/mainboard directory and on review.coreboot.org (search for HASWELL).
I have never heard of `igt_secure`. As you can access the dump, you can
at least build the payload yourself, and replace `fallback/payload` or add it under `img/`. Maybe that works. No idea if the keys/hashes verify anything from this.