* fix transpose conv,test=develop

* fix comments
test=develop

fix the bug of conv_transpose cudnn kernel: before version 1.6, the data_format is AnyLayout in inference model. When use version 1.6 and load the model which is saved by previous version, the error occurs.  This is because the cudnn kernel in version 1.6 is not compitable with Anylayout setting.

* Delete PadFuntion, include padding.h instead. test=develop

* move function(IsSymmetricPadding) from conv_cudnn_op.cu/conv_transpose_cudnn_op.cu to padding.h, test=develop