Add Google ChromeOS vendor support

Add Google ChromeOS vendor support

Google's ChromeOS can be booted super fast and safely
using coreboot. This adds the ChromeOS specific code that
is required by all ChromeBooks to do this.

Change-Id: Ic03ff090a569a27acbd798ce1e5f89a34897a2f2
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/817
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>