[coreboot] Flashrom as a payload with usb flash drive support

[Tadas Slotkus]

Hi, this is for testing. Works for me with seabios.
First optimize coreboot for your board, to get some space (remove
microcode updates or sth, we need about 60 KB).
Sorry haven't checked latest libpayload changes, so something might not
work.
I will write a blog post about this tomorrow.

Thanks,
Tadas Slotkus