sandbox: Enable support for MC34708 PMIC in DTS

This commit also provides the default values of the emulated MC34708 PMIC
internal registers content.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index 683b197..5a0f187 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -227,6 +227,10 @@
 		sandbox_pmic: sandbox_pmic {
 			reg = <0x40>;
 		};
+
+		mc34708: pmic@41 {
+			reg = <0x41>;
+		};
 	};
 
 	adc@0 {