dt-bindings: pinctrl: sunxi: Add A100 pinctrl bindings

Add device tree binding Documentation details for A100 pinctrl driver,
which has a r pin controller and a pin controller with more irq lines.

Signed-off-by: Yangtao Li <frank@allwinnertech.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/a5773d677bcc89af3810cdd187fae54eced82f27.1595572867.git.frank@allwinnertech.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>