gpio: max77620: add gpio driver for MAX77620/MAX20024

MAXIM Semiconductor's PMIC, MAX77620/MAX20024 has 8 GPIO
pins. It also supports interrupts from these pins.

Add GPIO driver for these pins to control via GPIO APIs.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>