drm/i915: Only include active engines in the capture state

Skip printing out idle engines that did not contribute to the GPU hang.
As the number of engines gets ever larger, we have increasing noise in
the error state where typically there is only one guilty request on one
engine that we need to inspect.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190808144511.32269-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gpu_error.h

@@ -81,7 +81,8 @@ struct i915_gpu_state {
 	struct intel_display_error_state *display;
 
 	struct drm_i915_error_engine {
-		int engine_id;
+		const struct intel_engine_cs *engine;
+
 		/* Software tracked state */
 		bool idle;
 		unsigned long hangcheck_timestamp;
@@ -158,7 +159,9 @@ struct i915_gpu_state {
 				u32 pp_dir_base;
 			};
 		} vm_info;
-	} engine[I915_NUM_ENGINES];
+
+		struct drm_i915_error_engine *next;
+	} *engine;
 
 	struct scatterlist *sgl, *fit;
 };