ARM: dts: imx6: phycore-som: add pmic onkey device

Without the onkey device it isn't possible to power off the system using
the X_PMIC_nONKEY signal which is routed to the SoM pin header.
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6qdl-phytec-phycore-som.dtsi

@@ -101,6 +101,10 @@ da9062_rtc: rtc {
 			compatible = "dlg,da9062-rtc";
 		};
 
+		da9062_onkey: onkey {
+			compatible = "dlg,da9062-onkey";
+		};
+
 		watchdog {
 			compatible = "dlg,da9062-watchdog";
 		};