pan/bi: Flesh out st_vary IR

We need to make the semantics of BI_VECTOR a bit more precise -
vectorize only the first argument, not all of them. This is enough for
current and future users, as far as I know.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4276>
4 files changed