dt-bindings: mtd: pl353-nand: Describe this hardware controller

Add a yaml description of this NAND controller which is described as a
subnode of the SMC bus.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/linux-mtd/20210610082040.2075611-18-miquel.raynal@bootlin.com