DRA72 and DRA718 EVM boards has a pcf8575 gpio expander
which is used for the LCD/LEDs and USB vbus detection.
Add the node for the pcf8575.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>