pan/bi: Use consistent modifier lists in packing

pan/bi: Use consistent modifier lists in packing

If there are modifiers only used by pseudo instructions, not the real
instructions, bi_packer can get out-of-sync with bi_opcodes, causing
hard-to-debug issues. Do the stupid-simple thing to ensure this doesn't happen.

This may be a temporary issue, depending whether ISA.xml and the IR get split
out for better Valhall support.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15223>