ARM: dts: rockchip: add power-domains property to dp node on rk3288

The clocks in the Rockchip rk3288 DisplayPort node are
included in the power-domain@RK3288_PD_VIO logic, but the
power-domains property in the dp node is missing, so fix it.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Link: https://lore.kernel.org/r/dab85bfb-9f55-86a1-5cd5-7388c43e0ec5@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>