[llvm] [AArch64][SLP] Add NFC test cases for floating point reductions (PR #106507)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

Can you explain what it is you plan to change? All the tests are `fast` and it might be something that needs to dependent on that.

https://github.com/llvm/llvm-project/pull/106507