* elementwise_add_grad Op optimization  (#29575)

* optimize for long width for elementwise (#29602)

* refine (#29622)

* delete the code for fp16 optimization because it is not faster than common template code (#29715)

* fix the shape choose of vectorize for cuda

* optimization for fp16 elementwise add (#29744)

* Fix the compiler error for half type (#29799)

* refine the compiler error for half2 operation (#29816)

* fix the compiler error when gcc4 cuda9.0 (#29997)