Extract out a helper to check for f16 formats from turnip so it can be
used elsewhere.
Signed-off-by: Rob Clark <rob.clark@oss.qualcomm.com>
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35589>