pinctrl: sunxi: Add support for interrupt debouncing

The pin controller found in the Allwinner SoCs has support for interrupts
debouncing.

However, this is not done per-pin, preventing us from using the generic
pinconf binding for that, but per irq bank, which, depending on the SoC,
ranges from one to five.

Introduce a device-wide property to deal with this using a microsecond
resolution. We can re-use the per-pin input-debounce property for that, so
let's do it!

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