pan/bi: Support the case where TEXC needs 0 or 1 staging reg

No need to add a COMBINE instruction if TEXC only needs zero or one
staging reg.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7206>
1 file changed