Created by: jacquesqiao

Base class that need to implement:

• MKLDNNLoDTensor derived from LoDTensor. in formal PaddlePaddle. Like MKLDNNMatrix.h for v2

• MKLDNNKernelBase derived from KernelBase. Like MKLDNNLayer.h in formal PaddlePaddle for v2

• Tensor transform functions used to tranform between LodTensor and MKLDNNKernel

Steps to add new kernel

Take pool_cudnn_op as example:

1. add pool_cudnn_op.cu.cc
2. implement PoolCUDNNOpKernel
3. register kernel with library type CUDNN

REGISTER_OP_KERNEL(pool2d, CUDNN, ::paddle::platform::CUDAPlace,
                   ops::PoolCUDNNOpKernel<float>,
                   ops::PoolCUDNNOpKernel<double>);

If we want to add pool_mkldnn kernel, the step should be:

1. add new file pool_mkldnn_op.cc
2. implement PoolMKLDNNOpKernel
3. register PoolMKLDNNOpKernel with library MKLDNN

REGISTER_OP_KERNEL(pool2d, MKLDNN, ::paddle::platform::MKLDNNPlace,
                   ops::PoolMKLDNNOpKernel<float>,
                   ops::PoolMKLDNNOpKernel<double>);