* move operators/math/math_function_* to pten/kernels/func
* namespace from `paddle::operators::math` to `pten::funcs`

* Migrate Dim and DDim from paddle::framework into pten namespace

* fix paddle::framework::Array

* fix framework::Array

* add two attributes for yolo box

* add scale_x_y for yolo_box, test=develop

* refine eps in iou_similarity, test=develop

* yolo_box OP add Attr(clip_bbox). test=develop

test=develop