dt-bindings: mtd: rockchip: add rockchip,rk3128-nfc

Add rockchip,rk3128-nfc compatible string.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/f09665c1-9938-38c1-9a31-f196a3ef9cf0@gmail.com