examples: Add RNN examples

[shu1chen]

Description

Add examples for Vanilla RNN and Linear-before-reset GRU RNN by referring to the RNN descriptions in oneDNN documentation. For lbr_gru, the gates order is update, reset and output gate, and there is an extra bias for u' gate.

Checklist

General

• [x] Do all unit and benchdnn tests (make test and make test_benchdnn_*) pass locally for each commit?
• [x] Have you formatted the code using clang-format?

[shu1chen]

Thanks for reviewing. I have updated the commit messages and also added reference to those examples in the documentation.