gpio: New driver for LSI ZEVIO SoCs

This driver supports the GPIO controller found in LSI ZEVIO SoCs.
It has been successfully tested on a TI nspire CX calculator.

Signed-off-by: Fabian Vogt <fabian@ritter-vogt.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>