Add pinctrl and gpio driver for Actions Semi S500 SoC.

The driver supports pinctrl, pinmux, pinconf, gpio and interrupt
functions using a set of registers shared between gpio and pinctrl.
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@gmail.com>
Link: https://lore.kernel.org/r/ce11c15f2f72798a8d740f8a7d5cbf1e6d70974a.1596461275.git.cristian.ciocaltea@gmail.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>