drm/i915/selftests: Take a breath during check_partial_mappings()

With kasan on a slow machine, it can take an age to check all the
partial mappings in a single iteration, so break it up with a
cond_resched) to avoid RCU stall reports.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190102114431.23022-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/selftests/i915_gem_object.c

@@ -238,6 +238,7 @@ static int check_partial_mapping(struct drm_i915_gem_object *obj,
 		u32 *cpu;
 
 		GEM_BUG_ON(view.partial.size > nreal);
+		cond_resched();
 
 		err = i915_gem_object_set_to_gtt_domain(obj, true);
 		if (err) {