drm/i915: extract hangcheck/reset/error_state state into substruct

This has been sprinkled all over the place in dev_priv. I think
it'd be good to also move all the code into a separate file like
i915_gem_error.c, but that's for another patch.

Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index ce1d074..d6b06aa 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1491,7 +1491,7 @@
 	struct drm_i915_private *dev_priv = ring->dev->dev_private;
 
 	ring->tail &= ring->size - 1;
-	if (dev_priv->stop_rings & intel_ring_flag(ring))
+	if (dev_priv->gpu_error.stop_rings & intel_ring_flag(ring))
 		return;
 	ring->write_tail(ring, ring->tail);
 }