[clang] [AArch64][Clang] Add support for __arm_agnostic("sme_za_state") (PR #121788)

[Benjamin Maxwell via cfe-commits]

https://github.com/MacDue approved this pull request.

LGTM, thanks for addressing my comments, just a minor nit-pick:

https://github.com/llvm/llvm-project/pull/121788