ARM: dts: am3517-evm: Add I/O expander for User DIP switches and LEDS

There is a tca6416 GPIO expander on i2c2. This patch enables the
GPIO expander which has several LED's and some connected DIP
switches

Signed-off-by: Derald D. Woods <woods.technical@gmail.com>
Signed-off-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>