dt-bindings: mtd: sunxi-nand: Add an example to validate the bindings

Copy-paste an existing DT node to ensure the dt_binding_check target
would catch any unforeseen difference.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/linux-mtd/20221114090315.848208-9-miquel.raynal@bootlin.com