pan/midgard: Schedule before RA

pan/midgard: Schedule before RA

This is a tradeoff.

Scheduling before RA means we don't do RA on what-will-become pipeline
registers. Importantly, it means the scheduler is able to reorder
instructions, as registers have not been decided yet.

Unfortunately, it also complicates register spilling, since the spills
themselves won't get bundled optimally and we can only spill twice per
ALU bundle (only one spill per bundle allowed here). It also prevents us
from eliminating dead moves introduced by register allocation, as they
are not dead before RA. The shader-db regressions are from poor spilling
choices introduced by the new bundling requirements. These could be
solved by the combination of a post-scheduler (to combine adjacent
spills into bundles) with a VLIW-aware spill cost calculation.
Nevertheless, the change is small enough that I feel it's worth it to
eat a tiny shader-db regression for the sake of flexibility.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>