Cache workspace size in the BenchmarkCache. (#15742)

Cache workspace size in the BenchmarkCache. (#15742)

Summary:
Cache the workspace size information for MIOpen for a given configuration as opposed to inquiring it every time. This reduces overhead significantly as inquiring the workspace size forces a full read of the performance database in MIOpen and this database has grown significantly in recent releases. This caching gets us back to ideal performance.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15742

Differential Revision: D13598932

Pulled By: bddppq

fbshipit-source-id: 4e65d247b71dec828293cf0562aac3fbd4fad83a