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

[David Green via cfe-commits]

davemgreen wrote:

> You could also create an ARM/ directory, and move arm-* files into that too (186 files)

Yeah - We might just need to be careful of tests that test both arm and aarch64 targets.
I noticed there are some arm64-* tests too that could be moved into the aarch64 directory.

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