On sequence end, if the last decoded picture is not output for rendering,
then the proxy surface is not created. In this case, the original surface
must be released explicitly to the context.
VA drivers may have a faster means to transfer user buffers to GPU
buffers than using memcpy(). In particular, on Intel Gen graphics, we
can use pwrite(). This provides for faster upload of bitstream and can
help higher bitrates.
vaapi_create_buffer() helper function was also updated to allow for
un-mapped buffers and pre-initialized data for buffers.
Keep a valid reference to the proxy in GstVaapiPicture so that frames
marked as "used for reference" could be kept during the lifetime of the
picture. i.e. don't release them too soon as they could be re-used right
away.
Drop obsolete gst_vaapi_decoder_push_surface() that was no longer used.
Change gst_vaapi_decoder_push_surface_proxy() semantics to assume PTS
is already set correctly and reference count increased, if necessary.
The new API simplifies a lot reference counting and makes it more
flexible for future additions/changes. The GstVaapiCodecInfo is
also gone. Rather, new helper macros are provided to allocate
picture, slice and quantization matrix parameter buffers.
