arm64: dts: rockchip: enable uart0 on Qnap-TS433

Uart0 is connected to an MCU on the board that handles system control
like the fan-speed. So far no driver for it is available though.

Tested-by: Uwe Kleine-König <ukleinek@debian.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20240723195538.1133436-4-heiko@sntech.de