ARM: dts: am335x-sl50: Enable the MCP23017 GPIO Expander.

Add support for the 16-Bit I/O Expander connected via the I2C bus.
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/am335x-sl50.dts

@@ -313,6 +313,10 @@ eeprom: eeprom@50 {
 		reg = <0x50>;
 	};
 
+	gpio_exp: mcp23017@20 {
+		compatible = "microchip,mcp23017";
+		reg = <0x20>;
+	};
 
 };