[clang] [test] Move CodeGen/aarch64-* into the AArch64 subfolder (PR #115818)

[Jonathan Thackray via cfe-commits]

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

Fine by me; I guess anyone with a PR in-flight will need to rebase.

https://github.com/llvm/llvm-project/pull/115818