dt-bindings: reset: npcm: Add support for NPCM8XX

Add binding document and device tree binding constants for Nuvoton BMC
NPCM8XX reset controller.

Signed-off-by: Tomer Maimon <tmaimon77@gmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>