drm/i915/selftests: Add a mock i915_vma to the mock_ring

Add a i915_vma to the mock_engine/mock_ring so that the core code can
always assume the presence of ring->vma.

Fixes: 8ccfc20a ("drm/i915/gt: Mark ring->vma as active while pinned")
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/20200114160030.2468927-1-chris@chris-wilson.co.uk
(cherry picked from commit b63b4fea)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/gt/mock_engine.c

@@ -59,11 +59,26 @@ static struct intel_ring *mock_ring(struct intel_engine_cs *engine)
 	ring->vaddr = (void *)(ring + 1);
 	atomic_set(&ring->pin_count, 1);
 
+	ring->vma = i915_vma_alloc();
+	if (!ring->vma) {
+		kfree(ring);
+		return NULL;
+	}
+	i915_active_init(&ring->vma->active, NULL, NULL);
+
 	intel_ring_update_space(ring);
 
 	return ring;
 }
 
+static void mock_ring_free(struct intel_ring *ring)
+{
+	i915_active_fini(&ring->vma->active);
+	i915_vma_free(ring->vma);
+
+	kfree(ring);
+}
+
 static struct i915_request *first_request(struct mock_engine *engine)
 {
 	return list_first_entry_or_null(&engine->hw_queue,
@@ -121,7 +136,7 @@ static void mock_context_destroy(struct kref *ref)
 	GEM_BUG_ON(intel_context_is_pinned(ce));
 
 	if (test_bit(CONTEXT_ALLOC_BIT, &ce->flags)) {
-		kfree(ce->ring);
+		mock_ring_free(ce->ring);
 		mock_timeline_unpin(ce->timeline);
 	}