pan/bi: Handle special ops in NIR->BIR

pan/bi: Handle special ops in NIR->BIR

Only on supported GPUs at the moment; for older Bifrost that don't
support these, I'm not sure yet where the right place to do the lowering
is. NIR algebraic rules would be "nice" but probably impractical -- but
it wouldn't be hard to do it directly in BIR (as a lowering pass or
alternative implementation).

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4139>