ARM: sun8i: a83t: Add device node for R_PIO

The A83T has 1 pingroup with 13 pins belonging to the R_PIO
or special pin controller.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>