benchmark

c7fd92c0 - Fix backward-compatiblity issue when mps was not available in pytorch (#1129)

Fix backward-compatiblity issue when mps was not available in pytorch (#1129) Summary: Old pytorch versions don't have the 'mps' backend. Therefore, we first detect whether it exists, then check if it is available. Pull Request resolved: https://github.com/pytorch/benchmark/pull/1129 Reviewed By: erichan1 Differential Revision: D38951684 Pulled By: xuzhao9 fbshipit-source-id: d8cbc9c5fec7c8f771b3a9a04487df2333a9bc4f