pinctrl: max77620: add pincontrol driver for MAX77620/MAX20024

MAXIM Semiconductor's PMIC, MAX77620/MAX20024 has 8 GPIO pins
which also act as the special function in alternate mode. Also
there is configuration like push-pull, open drain, FPS timing
etc for these pins.

Add pin control driver to configure these parameters through
pin control 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>