Created by: jczaja

This PR is introducing NHWC support for LRN and pool Grad ops of MKL-DNN as discussed at #20964

Note: There are changes in mean_op.cc and unused_var_check.cc that I would like @dzhwinter or @zhangting2020 or @sneaxiy to look at. Explanation is here: https://github.com/PaddlePaddle/Paddle/issues/20964#issuecomment-565508163