gallium/radeon: don't use the DMA ring for pipelined buffer uploads

gallium/radeon: don't use the DMA ring for pipelined buffer uploads

Submitting a DMA IB flushes the GFX IB and all GPU caches.

Vedran Miletić said:
  "On Tonga 380X, this improves The Talos Principle from 8.3 fps to 28.3 fps
   (all graphics settings Ultra, 4xAA, 1080p resolution with downsampling
   from 1200p)."

Some anonymous dude said:
   R9 390 results:
      Tomb Raider (normal settings): 80 -> 88 FPS
      Talos Principle (custom settings): 23 -> 56 FPS
      Metro Last Light Redux (default benchmark settings): 39 -> 40 FPS

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Tested-by: Vedran Miletić <vedran@miletic.net>
Tested-by: Grazvydas Ignotas <notasas@gmail.com>
Tested-by: Dieter Nützel <Dieter@nuetzel-hh.de>