drm/i915: Trim delays for wedging

CI still reports the occasional multi-second delay for resets, in
particular along the wedge+recovery paths. As the likely, and unbounded,
delay here is from sync_rcu, use the expedited variant instead.

Testcase: igt/gem_eio/unwedge-stress
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190219122215.8941-7-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_reset.c

@@ -830,7 +830,7 @@ static void __i915_gem_set_wedged(struct drm_i915_private *i915)
 	 * either this call here to intel_engine_write_global_seqno, or the one
 	 * in nop_submit_request.
 	 */
-	synchronize_rcu();
+	synchronize_rcu_expedited();
 
 	/* Mark all executing requests as skipped */
 	for_each_engine(engine, i915, id)