Update internal code for torch.linalg.solve (#56613)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56613
Replace linalg_solve_helper with `lu_stub` + `lu_solve_stub`.
Once `lu_stub` and `lu_solve_stub` have cuSOLVER-based codepath,
`torch.linalg.solve` will have it as well.
Test Plan: Imported from OSS
Reviewed By: albanD
Differential Revision: D28248766
Pulled By: mruberry
fbshipit-source-id: 3003666056533d097d0ad659e0603f59fbfda9aa
