* refine structure for cuda and rocm

* update

* update

* update

* update

* Add transfer_layout/dtype op

* clean useless codes

* fix unused var

* add optest in white.txt

* split into data_transfer.cc

* fix cmake

* modify according reviewer comment

* replace cast_op with transfer_dtype_op

* fix cast

* replace complex in set tensor from and to numpy

* replace complex template in cast op

* basic impl of type promote

* add comment & another testcase

* fix complex bugs & support python op promote type

* fix failed unittests & polish code

* add unittest for coverage

* change to only promote complex type

* polish code details

* polish several comments

Also add `elemwise_sub/mul/abs/clip` layers

There are mainly following fixes:

- take `DeviceContext` as the template parameter of math functors and OpKernel instead of `Place`
- remove `eigen_device` interface in base class  `DeviceContext`
- remove `GetEigenDevice` interface in `ExecutionContext` and base class `DeviceContext`
- remove unused `platform::EigenDeviceConverter`
- rename `REGISTER_OP_GPU_KERNEL` to `REGISTER_OP_CUDA_KERNEL`
- rename `USE_GPU_ONLY_OP` to `USE_CUDA_ONLY_OP`

* Cast Operator

Cast input variable to other data type

* Fix compile error

* Add cast op

* Follow comments