implement stack op createPlugin

paddle/fluid/inference/tensorrt/plugin/stack_op_plugin.h

@@ -121,7 +121,22 @@ class StackPluginV2Creator : public nvinfer1::IPluginCreator {
 
   nvinfer1::IPluginV2* createPlugin(
       const char* name, const nvinfer1::PluginFieldCollection* fc) override {
-    return nullptr;
+    int axis = -1;
+    int num_stack = -1;
+
+    for (int i = 0; i < fc->nbFields; ++i) {
+      const std::string name(fc->fields[i].name);
+      if (name == "axis") {
+        axis = static_cast<const int*>(fc->fields[i].data)[0];
+      } else if (name == "num_stack") {
+        num_stack = static_cast<const int*>(fc->fields[i].data)[0];
+      } else {
+        PADDLE_THROW(
+            platform::errors::Fatal("Meet an unknown plugin field '" + name +
+                                    "' when creating stack op plugin."));
+      }
+    }
+    return new StackPluginDynamic(axis, num_stack);
   }
 
   nvinfer1::IPluginV2* deserializePlugin(const char* name,