pinctrl: sunxi: Add Allwinner A31 pins set

The Allwinner A31 SoC uses the same IP than the one found in the
A10/A13, with only different pins. Add the pins and the associated
functions found in the A31.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>