i965: always run the post-RA scheduler

i965: always run the post-RA scheduler

Before, we would only do scheduling after register allocation if we
spilled, despite the fact that the pre-RA scheduler was only supposed to
be for register pressure and set the latencies of every instruction to
1. This meant that unless we spilled, which we rarely do, then we never
considered instruction latencies at all, and we usually never bothered
to try and hide texture fetch latency. Although a later commit removes
the setting the latency to 1 part, we still want to always run the
post-RA scheduler since it's able to take the false dependencies that
the register allocator creates into account, and it can be more
aggressive than the pre-RA scheduler since it doesn't have to worry
about register pressure at all.

Test                   master      post-ra-sched     diff       %diff
bench_OglPSBump2       396.730     402.386           5.656      +1.400%
bench_OglPSBump8       244.370     247.591           3.221      +1.300%
bench_OglPSPhong       241.117     242.002           0.885      +0.300%
bench_OglPSPom         59.555      59.725            0.170      +0.200%
bench_OglShMapPcf      86.149      102.346           16.197     +18.800%
bench_OglVSTangent     388.849     395.489           6.640      +1.700%
bench_trex             65.471      65.862            0.390      +0.500%
bench_trexoff          69.562      70.150            0.588      +0.800%
bench_heaven           25.179      25.254            0.074      +0.200%

Reviewed-by: Jason Ekstrand <jasoan.ekstrand@intel.com>