[SelectionDAG] Deprecate isNullValue and isAllOnesValue

This patch deprecates them as there are no known uses of these
functions in the project.

Differential Revision: https://reviews.llvm.org/D145357

llvm/include/llvm/CodeGen/SelectionDAGNodes.h

@@ -1608,10 +1608,10 @@ class ConstantSDNode : public SDNode {
 
   bool isOne() const { return Value->isOne(); }
   bool isZero() const { return Value->isZero(); }
-  // NOTE: This is soft-deprecated.  Please use `isZero()` instead.
+  LLVM_DEPRECATED("use isZero instead", "isZero")
   bool isNullValue() const { return isZero(); }
   bool isAllOnes() const { return Value->isMinusOne(); }
-  // NOTE: This is soft-deprecated.  Please use `isAllOnes()` instead.
+  LLVM_DEPRECATED("use isAllOnes instead", "isAllOnes")
   bool isAllOnesValue() const { return isAllOnes(); }
   bool isMaxSignedValue() const { return Value->isMaxValue(true); }
   bool isMinSignedValue() const { return Value->isMinValue(true); }