!15707 Enable acceleration by graph kernel for LSTM model.

From: @baita
Reviewed-by: @gaoxiong1,@dylangeng
Signed-off-by: @dylangeng

model_zoo/official/nlp/lstm/train.py

@@ -51,11 +51,16 @@ if __name__ == '__main__':
     parser.add_argument("--device_num", type=int, default=1, help="Use device nums, default is 1.")
     parser.add_argument("--distribute", type=str, default="false", choices=["true", "false"],
                         help="Run distribute, default is false.")
+    parser.add_argument("--enable_graph_kernel", type=str, default="true", choices=["true", "false"],
+                        help="Accelerate by graph kernel, default is true.")
+
     args = parser.parse_args()
 
+    _enable_graph_kernel = args.enable_graph_kernel == "true" and args.device_target == "GPU"
     context.set_context(
         mode=context.GRAPH_MODE,
         save_graphs=False,
+        enable_graph_kernel=_enable_graph_kernel,
         device_target=args.device_target)
 
     rank = 0