arm64: dts: rockchip: add #phy-cells to mipi-dsi1 on rk3399

arm64: dts: rockchip: add #phy-cells to mipi-dsi1 on rk3399

The dsi controller includes access to the dphy which might be used
not only for dsi output but also for csi input on dsi1, so add the
necessary #phy-cells to allow it to be used as phy.

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Tested-by: Sebastian Fricke <sebastian.fricke@posteo.net>
Acked-by: Helen Koike <helen.koike@collabora.com>
Link: https://lore.kernel.org/r/20210210111020.2476369-5-heiko@sntech.de
Signed-off-by: Heiko Stuebner <heiko@sntech.de>