Allwinner A10, A20 and R40 SoCs have similar GPIO layout.

Add SoC definitions in pinctrl-sunxi.h, in order to merge A20 support
into A10 driver, and add R40 support into it.
Signed-off-by: NIcenowy Zheng <icenowy@aosc.io>
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>