ARM: dts: imx6sx-sabreauto: add IO expander max7310 support

i.MX6SX Sabre Auto board has two max7310 IO expander on I2C3 bus, add
support for them.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>