We're failing a bunch of tests on G52 otherwise. Let's just disable this
feature on older gens for now, until we've gotten this fixed.
Fixes: 55c476efed ("panvk: advertise shaderFloat16")
Reviewed-by: Benjamin Lee <benjamin.lee@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33881>