freedreno/ir3: post-RA sched pass

freedreno/ir3: post-RA sched pass

After RA, we can schedule to increase parallelism (reduce nop's) without
worrying about increasing register pressure.  This pass lets us cut down
the instruction count ~10%, and prioritize bary.f, kill, etc, which
would tend to increase register pressure if we tried to do that before
RA.

It should be more useful if RA round-robin'd register choices.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3569>