Finally, you have to build coreboot with Memtest86+ as payload:
$ cd .. $ svn co svn://coreboot.org/coreboot/trunk coreboot $ cp memtest86+-4.20/memtest coreboot/payload.elf $ cd coreboot $ make menuconfig
Now enter the Payload menu and select Payload type and then An ELF executable payload file. Then, exit the menu, save your settings, and build coreboot:
The file build/coreboot.rom is your final coreboot image, which also contains the payload.