* fix rnn grad bug when num_layers is set 2 and dropout_prob is set 0

* add more test for rnn

* Modify relu native implementation

* fix GPU performance

* fix the rnn mask memory bug for out of read

* update the code for the rnn

Add eigen gru and fix the dropout bug in the rnn 

* add lstm, simple rnn op kernel

* fix the test_lstm for the rnn op

* change func name

* fix forward postprocess bug

* add gru forward, backward code

* remove unittest.skipIf; use a big rnn op instead of combination op

* fix input doesn't have gradient bug

* add eigen lstm forward, backward
Co-authored-by: Nwawltor <fangzeyang0904@hotmail.com>