dt-bindings: ata: Convert Allwinner AHCI controller to a schema

The Allwinner SoCs have a AHCI controllers that is supported in Linux, with
a matching Device Tree binding.

Now that we have the DT validation in place, let's convert the device tree
bindings for that controller over to a YAML schemas.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
[robh: 'maxItems: 1' for resets]
Signed-off-by: Rob Herring <robh@kernel.org>