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

[Sushant Gokhale via llvm-commits]

sushgokh wrote:

@davemgreen Thanks for the help. Yes, will add more tests( and change the costing as well for the next patch).

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