[llvm] [LLVM] Update AArch64 maintainers (PR #120440)

[Nikita Popov via llvm-commits]

nikic wrote:

@davemgreen I agree that it makes sense to merge the ARM and AArch64 maintainers, as there is a lot of overlap there. I went ahead and adopted your suggested list. It's a bit on the long side, but as long as most people have some kind of focus area it's probably okay.

https://github.com/llvm/llvm-project/pull/120440