Created by: tonyyang-svail

The current CopyFrom interface looks like this

https://github.com/PaddlePaddle/Paddle/blob/b28b2f172b2763dd8917833c2708309f98299a0a/paddle/framework/tensor_util.h#L31-L32

Since all device_context are globally accessible after https://github.com/PaddlePaddle/Paddle/pull/6537, we are able to refine the API to

inline void CopyFrom(const Tensor& src, Tensor* dst, const platform::Place& dst_place)