sandbox: dts: add meson secure monitor node

We need this to test UCLASS_SM.

Signed-off-by: Alexey Romanov <avromanov@salutedevices.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Link: https://lore.kernel.org/r/20230921081346.22157-4-avromanov@salutedevices.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index 6abce9e..ad20359 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -767,6 +767,10 @@
 				};
 			};
 		};
+
+		sm: secure-monitor {
+			compatible = "sandbox,sm";
+		};
 	};
 
 	fpga {