test: Add tests for the extcon

Provide tests to the simple extcon device.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index bcdea0b..453e53d 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -1816,6 +1816,10 @@
 		lba_shift = <9>;
 		lba = <2048>;
 	};
+
+	extcon {
+		compatible = "sandbox,extcon";
+	};
 };
 
 #include "sandbox_pmic.dtsi"