arm64: dts: rockchip: add fan support to rock-5a

Add the necessary DT changes for the Rock 5A board to enable support for
the PWM controlled heat sink fan.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20230710165228.105983-14-sebastian.reichel@collabora.com


Signed-off-by: Heiko Stuebner <heiko@sntech.de>