Reapply "Add support for single reductions in ComplexDeinterleavingPass (llvm#112875)"

This reverts commit 76714be.

Author: NickGuy-Arm

llvm/include/llvm/CodeGen/ComplexDeinterleavingPass.h

@@ -35,6 +35,7 @@ struct ComplexDeinterleavingPass
 enum class ComplexDeinterleavingOperation {
   CAdd,
   CMulPartial,
+  CDot,
   // The following 'operations' are used to represent internal states. Backends
   // are not expected to try and support these in any capacity.
   Deinterleave,
@@ -43,6 +44,7 @@ enum class ComplexDeinterleavingOperation {
   ReductionPHI,
   ReductionOperation,
   ReductionSelect,
+  ReductionSingle
 };
 
 enum class ComplexDeinterleavingRotation {