Patrick Georgi of Google's Chromium team added the Tegra "T210" a.k.a. Tegra X1 support to Coreboot. All of this new SoC enablement landed a short time ago with this Git commit.
The Tegra X1 hardware enablement was followed by the adding Smaug to Coreboot. Smaug is the codename for a Chrome OS device using the Tegra X1 but unfortunately details beyond that seem scarce.
So far only the Shield Android TV and Shield Portable use the Tegra X1, but damn, I can't wait for a Chromebook using the X1. The Tegra X1 packs in an ARMv8 64-bit Cortex-A57 + Cortex-A53 quad-core package in a big.LITTLE design while boasting NVIDIA Maxwell graphics. I also can't wait for a Tegra X1 development board similar to the Jetson TK1; I was told last month such a board like that might come in H2.