pan/bi: Don't duplicate texture op cases

pan/bi: Don't duplicate texture op cases

These two switches are redundant.

Furthermore, bi_tex_op could previously assume its input was a supported texop,
so it returned undefined values for unsupported texops. Now, without the guard
in front of it, bi_tex_op should check for supported texops, so we need to drop
the unsupported texops from the switch.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20906>