dt-bindings: mtd: mediatek: Reference raw-nand-chip.yaml

The mediatek NAND controller should reference the new raw-nand-chip.yaml
binding instead of the original nand-chip.yaml which does not contain
*all* the properties that may be used to fully describe the NAND
devices, certain properties being actually described under
nand-controller.yaml.

Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Cc: Xiangsheng Hou <xiangsheng.hou@mediatek.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/linux-mtd/20230619092916.3028470-16-miquel.raynal@bootlin.com