Cache results from SDPA.get_graph and bilinear_2d graph (#1911)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1911

This test is timing out a lot

executorch/backends/xnnpack/test:test_xnnpack_models - test_fp32_vit

https://www.internalfb.com/intern/test/844425039862774?ref_report_id=0

I did some profiling and looks like we are calculating this pattern over and over again for the unit test.

Let's try caching it

Reviewed By: kimishpatel, iseeyuan

Differential Revision: D53613581

fbshipit-source-id: 6e700a6e1fbdd8b291037d274022cf174f5878dd