dt-bindings: clock: nuvoton: add binding for ma35d1 clock controller

Add the dt-bindings header for Nuvoton ma35d1, that gets shared
between the clock controller and clock references in the dts.
Add documentation to describe nuvoton ma35d1 clock driver.

Signed-off-by: Jacky Huang <ychuang3@nuvoton.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>