dt-bindings: mtd: Describe Macronix NAND ECC engine

Describe Macronix NAND ECC engine. This engine may be used as an
external engine or can be pipelined with either a raw NAND controller or
a SPI controller. Both hardware designs with a SPI controller are shown
in the examples.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/linux-mtd/20211216111654.238086-11-miquel.raynal@bootlin.com