dma-buf: cleanup dma_buf_export() to make it easily extensible

At present, dma_buf_export() takes a series of parameters, which
makes it difficult to add any new parameters for exporters, if required.

Make it simpler by moving all these parameters into a struct, and pass
the struct * as parameter to dma_buf_export().

While at it, unite dma_buf_export_named() with dma_buf_export(), and
change all callers accordingly.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>

drivers/gpu/drm/armada/armada_gem.c

@@ -538,8 +538,14 @@ struct dma_buf *
 armada_gem_prime_export(struct drm_device *dev, struct drm_gem_object *obj,
 	int flags)
 {
-	return dma_buf_export(obj, &armada_gem_prime_dmabuf_ops, obj->size,
-			      O_RDWR, NULL);
+	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+
+	exp_info.ops = &armada_gem_prime_dmabuf_ops;
+	exp_info.size = obj->size;
+	exp_info.flags = O_RDWR;
+	exp_info.priv = obj;
+
+	return dma_buf_export(&exp_info);
 }
 
 struct drm_gem_object *