pinctrl: sunxi: Add A80 special pin controller

Like the previous designs, the A80 has a special pin controller for the
critical pins, like the PMIC bus.

Add a driver for this controller.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
[wens: Add A80 compatible strings to bindings doc; fix pin function
       names based on v1.3 datasheet; constify of_device_id table]
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>