drm/i915: Move common code out of i915_gpu_error.c

In the next patch, I want to conditionally compile i915_gpu_error.c and
that requires moving the functions used by debug out of
i915_gpu_error.c!

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161012090522.367-1-chris@chris-wilson.co.uk
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 124f464..36eff97 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -550,6 +550,9 @@
 
 int init_workarounds_ring(struct intel_engine_cs *engine);
 
+void intel_engine_get_instdone(struct intel_engine_cs *engine,
+			       struct intel_instdone *instdone);
+
 /*
  * Arbitrary size for largest possible 'add request' sequence. The code paths
  * are complex and variable. Empirical measurement shows that the worst case