[llvm] AArch64: Add tests for atomicrmw fp operations (PR #103701)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> We have a decent number of atomic tests in llvm/test/CodeGen/AArch64/Atomics, but I don't believe they include fp operations yet.

Grep doesn't find anything 

https://github.com/llvm/llvm-project/pull/103701