arm64: dts: nuvoton: Add initial ma35d1 device tree

Add initial device tree support for Nuvoton ma35d1 SoC, including
cpu, clock, reset, and serial controllers.
Add reference boards som-256m and iot-512m.

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