[llvm] [RISCV][TTI] Implement instruction cost for vp.reduce.* (PR #114184)

[Philip Reames via llvm-commits]

================
@@ -1179,6 +1179,79 @@ RISCVTTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
     return getCmpSelInstrCost(Instruction::Select, ICA.getReturnType(),
                               ICA.getArgTypes()[0], CmpInst::BAD_ICMP_PREDICATE,
                               CostKind);
+  case Intrinsic::vp_reduce_add:
----------------
preames wrote:

Please use:

```
Intrinsic::ID RedID = *VPI.getFunctionalIntrinsicID();
unsigned Opc = getArithmeticReductionInstruction(RedID);
OR
getMinMaxReductionIntrinsicOp(RedID);
```

https://github.com/llvm/llvm-project/pull/114184