[clang] [compiler-rt] [llvm] [AArch64][SME] Add support for sme-fa64 (PR #70809)

[Sander de Smalen via llvm-commits]

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

LGTM (with nit addressed), but please check with @ilinpv on the FMV priorities before merging the patch.

https://github.com/llvm/llvm-project/pull/70809