Insert the following snippet to /mingw/var/lib/mingw-get/data/profile.xml,
inside the <profile>-tag.
<repository uri="http://mingw.georgi-clan.de/%F.xml.lzma">
<package-list catalogue="coreboot-package-list" />
</repository>
Then run mingw-get update. After that, you have access to the coreboot packages: