The official name for the architecture after Valhall is 'Arm 5th
Gen'. In code we can use 'FIFTHGEN' or 'fifthgen', while in
documentation and printed output we should use 'Arm 5th Gen' or '5th
Gen'.
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/39267>