BFloat16: add explicit dtype support for to_mkldnn and to_dense (#48881)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/48881
Test Plan: Imported from OSS
Reviewed By: ngimel
Differential Revision: D25537190
Pulled By: VitalyFedyunin
fbshipit-source-id: a61a433c638e2e95576f88f081b64ff171b2316e
