freedreno/ir3: new pre-RA scheduler

freedreno/ir3: new pre-RA scheduler

This replaces the depth-first search scheduler with a more traditional
ready-list scheduler.  It primarily tries to reduce register pressure
(number of live values), with the exception of trying to schedule kills
as early as possible.  (Earlier iterations of this scheduler had a
tendency to push kills later, and in particular moving texture fetches
which may not be necessary ahead of kills.)

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4440>