[AArch64][NFC] Change order of instructions in isAssociativeAndCommutative

[AArch64][NFC] Change order of instructions in isAssociativeAndCommutative

Before this change, the order of instructions in `case` labels was
inconsistent. It is alphabetical order for FP instructions but another
order for integer instructions. This commit changes the order to
1) instruction set (base/FP/SIMD), 2) mnemonic, 3) element type.
I believe this change makes it consistent, improves understandability,
and makes it easy to add/remove a group of instructions.

Differential Revision: https://reviews.llvm.org/D139607