Add common GstVaapiCodecBase class
@gb
Submitted by Gwenole Beauchesne Link to original bug (#723285)
Description
Factor out common code and data from GstVaapiEncoder and GstVaapiDecoder into the GstVaapiCodecBase class. On the data size, at the minimum, this object shall include GstvaapiDisplay, va_display, GstVaapiContext, va_context, GstVaapiCodec, GstVideoInfo. On the API side, the minimum functions are refcounting related, and start()/stop() [new] semantics.