ci: Build kernels and rootfs for x86 devices

For testing Mesa on LAVA devices with the amd64 architecture, build
kernels and rootfs in the same way as we do for arm64 and armhf.

Also add a few trivial jobs for a specific AMD Chromebook.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Rohan Garg <rohan.garg@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5903>
14 files changed