Move SDPA decomp pass from Qualcomm's directory to be shareable and call it for Cadence backends (#4258)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/4258

Moving the pass to backends/transforms so that other backends can call it, and call it from the Cadence side so that we can quantize the bmm ops in SDPA.

Reviewed By: cccclai

Differential Revision: D59600486

fbshipit-source-id: c5e3209be1d3af89903ab31c3c13d2b0e9a23925