Refactor CUDA callback functor

[sryap]

Summary: This diff creates a common CUDA callback function, called cuda_callback_func, in the kv_db_utils namespace. It can be used as a callback function for cudaStreamAddCallback.

cuda_callback_func casts the input functor into a void function, invokes it and then delete it.

Differential Revision: D60348604

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This pull request was exported from Phabricator. Differential Revision: D60348604

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This pull request was exported from Phabricator. Differential Revision: D60348604

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This pull request was exported from Phabricator. Differential Revision: D60348604

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This pull request has been merged in pytorch/FBGEMM@9851079b0aa38031e549c2ed4571909764009b78.