Upgrade MKLDNN to v0.20.5 (#25757)
Summary:
1. Fix issues exposed by below posts.
https://github.com/pytorch/pytorch/issues/25242
https://github.com/pytorch/pytorch/issues/25101
https://github.com/pytorch/pytorch/issues/23825
2. Fix RNN support issue in mkldnn-bridge
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25757
Differential Revision: D17367948
Pulled By: VitalyFedyunin
fbshipit-source-id: d8430d3909ecbf853afa0ce3d968735f86f1da31
