drm/i915: Check whether chip is wedged in i915_wait_request()

i915_wait_request() only checks mm.wedged after it interacts with the
hardware, generally causing the driver to lock up waiting for a wedged
chip. Make sure we check mm.wedged as the first thing we do.
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ben Gamari <bgamari.foss@gmail.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/gpu/drm/i915/i915_gem.c

@@ -1751,6 +1751,9 @@ i915_wait_request(struct drm_device *dev, uint32_t seqno)
 
 	BUG_ON(seqno == 0);
 
+	if (dev_priv->mm.wedged)
+		return -EIO;
+
 	if (!i915_seqno_passed(i915_get_gem_seqno(dev), seqno)) {
 		if (IS_IGDNG(dev))
 			ier = I915_READ(DEIER) | I915_READ(GTIER);