Modify the dropout op to multi-thread (#19504)

* Modify the dropout op to multi-thread
test=develop

* define parallel
test=develop

paddle/fluid/operators/dropout_op.h

@@ -76,14 +76,21 @@ class CPUDropoutKernel : public framework::OpKernel<T> {
           }
         }
       }
+    } else {
+      if (upscale_in_train) {
+        const auto* X_data = x->data<T>();
+        auto* Y_data = y->mutable_data<T>(context.GetPlace());
+#ifdef PADDLE_WITH_MKLML
+#pragma omp parallel for
+#endif
+        for (int i = 0; i < x->numel(); i++) {
+          Y_data[i] = X_data[i];
+        }
       } else {
         auto X = EigenMatrix<T>::Reshape(*x, 1);
         auto Y = EigenMatrix<T>::Reshape(*y, 1);
         auto& place =
             *context.template device_context<DeviceContext>().eigen_device();
-      if (upscale_in_train) {
-        Y.device(place) = X;
-      } else {
         Y.device(place) = X * static_cast<T>(1.0f - dropout_prob);
       }
     }