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 (closed).