freedreno/ir3: fix kill scheduling
kill (and other cat0/flow instructions) do not have a dst register.
Which was mostly harmless before, other than RA thinking it would need
a free register to write. (But nothing consumed it, so the value would
be immediately dead.) But this would cause more problems with postsched
which would see a bogus dependency.
Also, post-RA sched *does* need to see the dependency on the predicate
register.
Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3569>