ARM: dt: tegra: whistler: configure power off

Add DT property to tell the MAX8907 that it should provide the
pm_power_off() implementation. This allows "shutdown" to work.
Signed-off-by: NStephen Warren <swarren@nvidia.com>

arch/arm/boot/dts/tegra20-whistler.dts

@@ -267,6 +267,8 @@
 			reg = <0x3c>;
 			interrupts = <0 86 0x4>;
 
+			maxim,system-power-controller;
+
 			mbatt-supply = <&usb0_vbus_reg>;
 			in-v1-supply = <&mbatt_reg>;
 			in-v2-supply = <&mbatt_reg>;