Actually no. We've demonstrated this on boards without using coreboot support such as OCP's Winterfell machine. The reason is that we're inserting the Linux kernel in UEFI's DXE stage, whereas cpu init such as memory training are still handled by UEFI's PEI stage. From the perspective of UEFI, the Linux kernel is just another DXE to execute.
The current way an x86 platform is booted to linux today uses mostly closed source UEFI DXE drivers, so the current boot flow is really (simplified) like this:
UEFI DXE loads disk/network -> Linux
We're doing
Linux (with commonly used open source drivers)-> Linux
It's possible that if your end goal is a Linux system without too many requirements, you could stop at the first Linux system without ever booting the second. However the bios rom memory is pretty small, and we're mostly working with about 4-8mb of free space left not including the ME region or UEFI PEI.
I don't know of any easily digestible document though.