dt-bindings: pinctrl: add compatible string for Allwinner V3 pinctrl

The Allwinner V3 SoC, despite come with the same die with V3s, has more
GPIO pins than V3s, and a different compatible string for pinctrl is
needed.

Add the compatible string for V3 pinctrl.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>