pan/bi: Handle fmov class ops

pan/bi: Handle fmov class ops

We need to lower them to something reasonable (ideally, the modifier
would be attached but we need to do something for the case it's not). We
specifically have to lower pre-sched as well, but we can do the lower
literally at schedule time for now (if this proves annoying, we can move
it earlier, but I want to leave room for modifier-aware copyprop should
that prove interesting).

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4396>