pinctrl: axp209: Add support for GPIO3 on the AXP209

The AXP209 device has a 4th GPIO which has a slightly different register
setup, where the control + status bits are held in a single register
rather than sharing AXP20X_GPIO20_SS with GPIOs 0-2.

Signed-off-by: Jonathan McDowell <noodles@earth.li>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/dde40307f0ebc23b9841c32e702b481ab5193dc4.1684258957.git.noodles@earth.li


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>