ARM: dts: imx6ul-liteboard: Support poweroff

Support proper system power-off, which disables main regulator. This
results in much lower power consumption and support of power-on issued
by button press.

Signed-off-by: Marcin Niestroj <[e-mail]>
Signed-off-by: Shawn Guo <[e-mail]>

arch/arm/boot/dts/imx6ul-liteboard.dts

···
 	};
 };
 
+&snvs_poweroff {
+	status = "okay";
+};
+
 &uart1 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_uart1>;