* refactor register mechanism, current so size: 1.20MB. test=develop

* fix KernelRegistry::Global().Create. test=develop

* fix cpplint errors. test=develop

* fix test_subgraph_pass bug. test=develop

* register kernel with target,precision,datalayout combination. test=develop

* fix test_paddle_api no op found bug. test=develop

* enhance comment

* fix lite/kernels/arm/elementwise_compute_test.cc. test=develop

* fix code style

* revert format of unchanged files. test=develop

* fix code format according to cpplint 1.5.1. test=develop

* remove redundant include header. test=develop

* update x86 op and kernel to run content-dnn model test=develop

* [X86] add attention_padding_mask op, x86 kernel and unit test

test=develop

* [CUDA] add attention_padding_mask cuda kernel and unit test

test=develop