ARM: dts: sunxi: Remove pinctrl groups setting bias

So far we've enabled pull-up and pull-down resistors on GPIOs using a
pinctrl node. Now that the GPIO binding allows for a flag to declare this,
let's switch to it.

This brings us closer to removing all the GPIO pinctrl nodes, which will in
turn allow us to switch the pinctrl strict mode on.

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