drm/i915: If the GPU hangs twice within 5 seconds, declare it wedged.

The issue is that we may become stuck executing a long running shader
and continually attempt to reset the GPU. (Or maybe we tickle some bug
and need to break the vicious cycle.) So if we are detect a second hang
within 5 seconds, give up trying to programme the GPU and report it
wedged.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index d19a26a..73ad8bf 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -699,6 +699,8 @@
 	struct drm_mm_node *compressed_fb;
 	struct drm_mm_node *compressed_llb;
 
+	unsigned long last_gpu_reset;
+
 	/* list of fbdev register on this device */
 	struct intel_fbdev *fbdev;
 } drm_i915_private_t;