PR #62817: [onednn] Enable auto_mixed_precision for fp16 on cpu
PR #62817: [onednn] Enable auto_mixed_precision for fp16 on cpu

Imported from GitHub PR https://github.com/tensorflow/tensorflow/pull/62817

This PR enables AMP FP16 on supporting Intel Xeon CPUs. If there is no GPU available to run FP16, it checks if FP16 can be executed on CPU.
Use config `auto_mixed_precision`  to enable FP16 on CPUs.
Copybara import of the project:

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fc1ee3bcc2d07d30bcd9480280796eb014bb0e2b by Gauri1 Deshpande <gauri1.deshpande@intel.com>:

[onednn] Enable auto_mixed_precision for fp16 on cpu

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9a3c8d59eb65fac7253b8f9a0db92dc93e22e374 by Gauri1 Deshpande <gauri1.deshpande@intel.com>:

Address review comments - update comments as per guidelines.

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27b1a9623f72a5acd13a864d1d00b47a85ca43fe by Gauri1 Deshpande <gauri1.deshpande@intel.com>:

Address review comments

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9a3ef902974965aacfaf2192b3a7253dcd0609f8 by Gauri1 Deshpande <gauri1.deshpande@intel.com>:

Address review comments

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0ab5b80f9bf952e3eb6f5fb1df0881be7cdd0959 by Gauri1 Deshpande <gauri1.deshpande@intel.com>:

minor change

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182a17386f94f26fa7f9753eb03ea0b6263ef8b6 by Gauri1 Deshpande <gauri1.deshpande@intel.com>:

Address review comments

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9780d75ad68275bf30b81c7cf02688fb87e5f1e2 by Gauri1 Deshpande <gauri1.deshpande@intel.com>:

Address re-review comments

Merging this change closes #62817

FUTURE_COPYBARA_INTEGRATE_REVIEW=https://github.com/tensorflow/tensorflow/pull/62817 from Intel-tensorflow:gaurides/amp_fp16 9780d75ad68275bf30b81c7cf02688fb87e5f1e2
