Adding MKL DNN license from Intel's repo

[sadatnfs]

Adding the LICENSE file so that third_party/mkl_dnn LICENSE file is picked up upon MKL configured build.

This build works now in a Docker (refer to #20811), where initially the missingness of the MKL-DNN LICENSE file would error out since commit #20576 forces the check for the DNN license.

bazel build --config=opt --config=mkl \
    tensorflow/tools/pip_package:build_pip_package 

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[sadatnfs]

I signed it!

[googlebot]

CLAs look good, thanks!

[qlzh727]

Please update this place holder accordingly

[mahmoud-abuzaina]

@qlzh727 I think this is meant to be a template and not having actual values.

[sadatnfs]

@qlzh727 hmm it looks like the MKL LICENSE file in third_party/mkl/LICENSE also has the two fileds as blank. We should be consistent with that eh?

[qlzh727]

I think they they should be consistent. Also waiting for input from @martinwicke who probably have more detailed knowledge.

[sadatnfs]

Hmm is there a reason why import/copybara check failed?

[qlzh727]

@yifeif, not sure why copybara is not porting the PR to internal.

[yifeif]

Discussed offline with @qlzh727. Fixed now.