dt-bindings: memory-controllers: nuvoton: Add NPCM memory controller

Add dt-bindings document for Nuvoton NPCM memory controller.

Signed-off-by: Marvin Lin <milkfafa@gmail.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230111093245.318745-3-milkfafa@gmail.com