pan/va: Split out compare instructions

pan/va: Split out compare instructions

The different combine modes form different instructions from each other and in
particular from the two-source version on Bifrost. Model them as such so we can
represent the relevant Valhall-specific lowering/optimizations accurately in the
compiler.

This requires updating the unit tests to use the new names since there's not
much point keeping around the aliases.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17794>