gitlab-ci: re-enable mali400/450 and t820 jobs

gitlab-ci: re-enable mali400/450 and t820 jobs

The FILES_HOST_NAME and FILES_HOST_URL are in the baylibre's runner
environment to make it more flexible.

Also use the new aarch64 mesa-ci-aarch64-lava-baylibre runner with
embedded nginx server to serve the LAVA artifacts.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4295>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4295>