[oneDNN]: Adding a build flag to conditionally compile with oneDNN v3.x
@penpornk I have addressed your review comments. Can you please take a look? Hi @penpornk Can you please review this PR ? Thank you! @penpornk Gentle reminder for PR review. Please let me know if you have any questions. Thanks. @penpornk  Thanks for the PR review. I have addressed all your review comments. Can you please take a look? Closing the PR since it has been merged in https://github.com/tensorflow/tensorflow/commit/2802c538daff0ad369c8c8243f1f0f9b605f51d1.
This PR adds a build flag to conditionally compile with oneDNN v3.x. It also adds support for oneDNN v3.x in `mkl_util.h`.

To build with oneDNN v3.x, pass `--config=mkl --define=build_with_onednn_v3=true --define=build_with_onednn_v2=false`.