va: basedec: Select output format with the used chroma in decoder.

Currently, video format is decided with downstream caps intersection, but that's not correct since chroma is not considered. The video decoders have to decide the output format given the used chroma, not by the downstream caps negotiation.

This patch changes that. Still, caps feature is selected by caps negotiation, then, with the preferred caps feature, the output format is search within that caps feature.