test: dm: Add test for ofnode options phandle helper

Add test for ofnode options phandle helper and add new property in the
sandbox test dts.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index b8a4646..1ffa64a 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -106,6 +106,7 @@
 			testing-bool;
 			testing-int = <123>;
 			testing-str = "testing";
+			testing-phandle = <&phandle_node_1>;
 		};
 	};