ARM: dts: da850-lego-ev3: Add node for reboot modes

This adds a new node for reboot modes on LEGO MINDSTORMS EV3. The EV3's
bootloader looks for a magic number in the ARM local RAM and if found,
it will boot into a special firmware update mode where the flash memory
can be written via USB.

This has been testing working using the command:

    # systemctl reboot loader
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>

arch/arm/boot/dts/da850-lego-ev3.dts

@@ -184,6 +184,23 @@ battery {
 		io-channel-names = "voltage", "current";
 		rechargeable-gpios = <&gpio 136 GPIO_ACTIVE_LOW>;
 	};
+
+	/* ARM local RAM */
+	memory@ffff0000 {
+		compatible = "syscon", "simple-mfd";
+		reg = <0xffff0000 0x2000>; /* 8k */
+
+		/*
+		 * The I2C bootloader looks for this magic value to either
+		 * boot normally or boot into a firmware update mode.
+		 */
+		reboot-mode {
+			compatible = "syscon-reboot-mode";
+			offset = <0x1ffc>;
+			mode-normal = <0x00000000>;
+			mode-loader = <0x5555aaaa>;
+		};
+	};
 };
 
 &pmx_core {