dt-bindings: display: rockchip,dw-hdmi: add power-domains property

Most Rockchip hdmi nodes are part of a power domain.
Add a power-domains property and include it to the example
with some reordering to align with the (new) documentation
about property ordering.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/5c45527a-e218-40a3-8e71-a5815417e5f7@gmail.com