r600/sfn: Add GS thread with bo output fix

The old code does the same for R600.

Fixes: 33765aa9
     r600/sfn: Enable NIR for pre RG hardware

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
86 jobs for !17880 with r600-nir-pre-eg in 7 seconds (queued for 15 seconds)
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