drm/driver: Add defaults for .gem_prime_export/import callbacks

The majority of drivers use drm_gem_prime_export() and
drm_gem_prime_import() for these callbacks so let's make them the
default.

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181110145647.17580-2-noralf@tronnes.org
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 8d54d51..ba6c7e0 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -529,7 +529,10 @@ static struct dma_buf *export_and_register_object(struct drm_device *dev,
 		return dmabuf;
 	}
 
-	dmabuf = dev->driver->gem_prime_export(dev, obj, flags);
+	if (dev->driver->gem_prime_export)
+		dmabuf = dev->driver->gem_prime_export(dev, obj, flags);
+	else
+		dmabuf = drm_gem_prime_export(dev, obj, flags);
 	if (IS_ERR(dmabuf)) {
 		/* normally the created dma-buf takes ownership of the ref,
 		 * but if that fails then drop the ref
@@ -762,7 +765,10 @@ int drm_gem_prime_fd_to_handle(struct drm_device *dev,
 
 	/* never seen this one, need to import */
 	mutex_lock(&dev->object_name_lock);
-	obj = dev->driver->gem_prime_import(dev, dma_buf);
+	if (dev->driver->gem_prime_import)
+		obj = dev->driver->gem_prime_import(dev, dma_buf);
+	else
+		obj = drm_gem_prime_import(dev, dma_buf);
 	if (IS_ERR(obj)) {
 		ret = PTR_ERR(obj);
 		goto out_unlock;