[llvm] [AArch64][SME] Enable subreg liveness tracking when SME is available (PR #92142)

[Sander de Smalen via llvm-commits]

https://github.com/sdesmalen-arm approved this pull request.

>From a quick scan of the tests I couldn't see anything unexpected.
LGTM.

https://github.com/llvm/llvm-project/pull/92142