va: caps: Don't use image formats for decoded frames.
Initially we tried to use the internal color conversion used in i965 and Gallium drivers when decoding. But this approach has showed limitations and problems.
This patch removes completely the possible color conversion at decoding, since it show problems with deinterlacing, for example:
gst-launch-1.0 filesrc location=interlaced.mpg2 ! parsebin ! vampeg2dec ! vadeinterlace ! xvimagesink
Allowing only the surface formats when decoding is more stable.
For color conversion is better to do it explicitly with vapostproc.