The driver missed an of_xlate function to translate gpio numbers
as found in the DT to the correct chip and number.
While there I've set #gpio_cells to a fixed value of 2.
I've used gpio-pxa.c as template for those changes and tested my changes
successfully on a da850 board using entries for gpio-leds in a DT. So I didn't
reinvent the wheel but just copied and tested stuff.
Thanks to Grygorii Strashko for the hint to the existing code in gpio-pxa.