handle U/V plane locally & use chroma description in picture_UpdatePlanes()

In most cases the U/V plane swapping can be handled locally and we don't need the core to tell us about a single case that exists anymore.

After this cleanup, picture_UpdatePlanes() is simplified and can just use the same plane filling code as picture_Setup(). It's only used by D3D code to map GPU resources locked to the CPU into VLC planes.