ARM: dts: imx7s: Add snvs-poweroff support

Just like other i.MX devices, i.MX7 also supports using the SNVS
block to poweroff the chip.

Add an entry for it.
Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/nxp/imx/imx7s.dtsi

@@ -636,6 +636,15 @@ snvs_rtc: snvs-rtc-lp {
 					clock-names = "snvs-rtc";
 				};
 
+				snvs_poweroff: snvs-poweroff {
+					compatible = "syscon-poweroff";
+					regmap = <&snvs>;
+					offset = <0x38>;
+					value = <0x60>;
+					mask = <0x60>;
+					status = "disabled";
+				};
+
 				snvs_pwrkey: snvs-powerkey {
 					compatible = "fsl,sec-v4.0-pwrkey";
 					regmap = <&snvs>;