drm/i915: Disable hangcheck when wedged

If the gpu reset fails and the machine is terminally wedged, further
hangchecks achieve nothing but noise. Disable them, with a corollary
that we re-enable hangchecking after a successful GPU reset in case the
user is artificially bringing the machine back to life through the debug
interface.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161122144121.7379-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.c

@@ -1822,6 +1822,8 @@ void i915_reset(struct drm_i915_private *dev_priv)
 		goto error;
 	}
 
+	i915_queue_hangcheck(dev_priv);
+
 wakeup:
 	wake_up_bit(&error->flags, I915_RESET_IN_PROGRESS);
 	return;