Add the Video Processing Unit node for the RK3399 SoC.

Also, fix the VPU IOMMU node, which was disabled and lacking
its power domain property.
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>