Support was added to Coreboot on Saturday that provides Kconfig options for Linux as a payload. Coreboot uses Kconfig (commonly known as the configuration system for the Linux kernel) as its method of configuring the open-source firmware's different options and support targets. The new Kconfig options that were added allow for users/developers to define the Linux kernel image, initrd, and any command-line parameters to be passed to the kernel.
The commit adding these kernel options to the Coreboot Kconfig system can be found via Gitweb. For those wanting to learn more about Coreboot's different payload options, see this Wiki page.