inductor: disable lowmem_dropout on CPU (#100702)
In https://github.com/pytorch/pytorch/pull/97002, we fall back bernoulli and disabled lowmem_dropout on CPU, which brings significant performance improvements for both bernoulli and dropout.
PR https://github.com/pytorch/pytorch/pull/97931 disabled lowmem_dropout by default, thus removed the code that disabled lowmem_dropout on CPU, but unfortunately, it introduced performance regression on CUDA (https://github.com/pytorch/pytorch/issues/98614). Then https://github.com/pytorch/pytorch/pull/98631 reenabled lowmem_dropout by default.
As a result, the performance of dropout on CPU has decreased since https://github.com/pytorch/pytorch/pull/98631. This pr re-added the code to disable lowmem_dropout on CPU.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100702
Approved by: https://github.com/jgong5, https://github.com/ngimel
