[llvm] [AArch64] Re-enable rematerialization for streaming-mode-changing functions. (PR #83235)

[Paul Walker via llvm-commits]

paulwalker-arm wrote:

The approach looks sensible to me.  I do think we should roll out the `VG` change across the other instructions, or at least those that directly access `VG` like `ADDVL`, but agree that's better done as follow on work.

https://github.com/llvm/llvm-project/pull/83235