[pt2][inductor] move gemm local cache to `cache_dir()/cache/{hash}` (#105334)
Summary: move gemm autotuning local cache to `cache_dir()/cache/{hash}` since we might have multiple local caches, i.e. one cache with `allow_tf32=True` and one cache with `allow_tf32=False`
Test Plan: sandcastle + CI
Differential Revision: D47504654
Pull Request resolved: https://github.com/pytorch/pytorch/pull/105334
Approved by: https://github.com/jansel
