arm64: dts: rockchip: add rk3399 DSI0 reset

We've documented this one already, but we didn't add it to the DTSI yet.

Suggested-by: Nickey Yang <nickey.yang@rock-chips.com>
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>