Add bfloat16 to CPU cauchy_kernel, log_normal_kernel, exponential_kernel (#38427)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/38427
Test Plan: Imported from OSS
Differential Revision: D21640640
Pulled By: pbelevich
fbshipit-source-id: 9cff8f6b5c33b3b31753c76fc8033d329b218019
