ac/nir: use ordered float comparisons except for not equal

ac/nir: use ordered float comparisons except for not equal

Original patch from Timothy Arceri, I have just fixed the
not equal case locally.

This fixes one important rendering issue in Wolfenstein 2
(the cutscene transition issue).

RadeonSI uses the same ordered comparisons, so I guess that
what we should do as well.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104302
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104905
Cc: <mesa-stable@lists.freedesktop.org>
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>