lima/gpir: Do all lowerings before rsched

lima/gpir: Do all lowerings before rsched

The scheduler assumes that load nodes are always duplicated so that they
can always be scheduled eventually and therefore they never need to be
spilled. But some lowerings were running after the pre-RA scheduler,
whereas duplication has to happen before then since it's needed for the
scheduler to do a better job reducing register pressure. This meant
that lowerings were introducing multiple uses of a load instruction,
which broke the scheduler's expectation and resulted in infinite loops
in situations where the only nodes available to spill were load nodes.
Spilling load nodes would be silly, so we want to fix the lowerings
rather than the scheduler. Just do all lowerings before the pre-RA
scheduler, which also helps with reducing pressure since the scheduler
can more accurately compute the pressure.

Fixes lima/mesa#104.

Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Tested-by: Vasily Khoruzhick <anarsoul@gmail.com>