pinctrl: sunxi: Deprecate sunxi pinctrl bindings

The generic pin configuration and multiplexing should be preferred now,
even though we still support the old one.

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