arm64: dts: rockchip: add fan on rk3399-sapphire board

The Sapphire board has a 12V fan. So, adding it to the DTS.
There is no power supply directly connected, it needs the baseboard to
work.
If the board is used standalone then a hardware modification is needed.
On the Sapphire board there is an unpopulated resistor to connect it to
VBUS_TYPEC, which is usually 5V (too low) and can range up to 20V
(too high).
I tested it for a week connected to VCC_SYS which is 8.4V and proved to
be more than enough for the required cooling needs. This is the
connection described in the comment.

Signed-off-by: Vicente Bergas <vicencb@gmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>