[llvm] [AArch64] Combine separate vector and scalar tablegen SDNode record for AArch64ISD::REV16. NFC (PR #125614)

[Sergei Barannikov via llvm-commits]

s-barannikov wrote:

Note that this makes the vector case less constrained (and inconsistent with REV32/REV64, which are vector-only). I think it would be better to introduce a new enum value for the scalar case.
Is is only used in [one](https://github.com/llvm/llvm-project/blob/8017ca1d0056907331ff7542ac9ff1ff5ec969a2/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp#L22497) place.


https://github.com/llvm/llvm-project/pull/125614