ARM: dts: am57xx: cl-som-am57x: add I2C3 support

Enable I2C3 bus and add appropriate pinmux.

Signed-off-by: Dmitry Lifshitz <lifshitz@compulab.co.il>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Tony Lindgren <tony@atomide.com>