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

[Kerry McLaughlin via llvm-commits]

kmclaughlin-arm wrote:

Using the LNT test suite, I took some measurements to understand the impact on compile-time and found that enabling this generally for AArch64 results in about a 0.1% increase based on instruction count. Many of the AArch64 test files require updating, but I don't think there are any functional issues exposed with these changes.

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