st/va: properly defines VAImageFormat formats and improve VaCreateImage

st/va: properly defines VAImageFormat formats and improve VaCreateImage

Added PIPE_VIDEO_CHROMA_FORMAT_NONE in p_format.h
and return it by default in ChromaToPipe.

Renamed YCbCrToPipe to VaFourccToPipeFormat because it now
contains RGB.

Implemented PipeFormatToVaFourcc which will be used later in
VlVaDeriveImage.

Note that gstreamer-vaapi check all the VAImageFormat fields.

Signed-off-by: Julien Isorce <j.isorce@samsung.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>