i965: Avoid kernel BUG_ON if we happen to wait on the pipe_control w/a BO.

For this and occlusion queries, we're trying to avoid setting
I915_GEM_DOMAIN_RENDER for the write domain, because the data written
is definitely not going through the render cache, but we do need to
tell the kernel that the object has been written.  However, with using
I915_GEM_DOMAIN_GTT, the kernel on retiring the batchbuffer sees that
the w/a BO has a write domain of GTT, and puts it on the flushing
list.  If something tries to wait for that BO to finish rendering
(such as the AUB dumper reading the contents of BOs), we get into
wait_request (since obj->active) but with a 0 seqno (since the object
is on the flushing list, not actually on a ringbuffer), and BUG_ONs.

To avoid the kernel bug (which I'm hoping to delete soon anyway), just
use I915_GEM_DOMAIN_INSTRUCTION like occlusion queries do.  This
doesn't result in more flushing, because we invalidate INSTRUCTION on
every batchbuffer now that we're state streaming, anyway.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Tested-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/intel/intel_batchbuffer.c

@@ -325,7 +325,7 @@ intel_emit_post_sync_nonzero_flush(struct intel_context *intel)
    OUT_BATCH(_3DSTATE_PIPE_CONTROL);
    OUT_BATCH(PIPE_CONTROL_WRITE_IMMEDIATE);
    OUT_RELOC(intel->batch.workaround_bo,
-	     I915_GEM_DOMAIN_GTT, I915_GEM_DOMAIN_GTT, 0);
+	     I915_GEM_DOMAIN_INSTRUCTION, I915_GEM_DOMAIN_INSTRUCTION, 0);
    OUT_BATCH(0); /* write data */
    ADVANCE_BATCH();