st/va: force to flush the last p frame in idr period

During dual instance encoding submission, if the second encode task and first
encode task have no reference dependency, e.g. p following with idr-frame,
there is a chance the second task will use for its reconstructed picture
buffer the same buffer used by first task for its reference/reconstructed
picture. In this case, buffer corruption may occur depending on encoding
speed. Fix is to force flush these two tasks separately to avoid race condition

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=98005

Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>

src/gallium/state_trackers/va/picture.c

@@ -578,6 +578,9 @@ vlVaEndPicture(VADriverContextP ctx, VAContextID context_id)
    }
 
    context->decoder->end_frame(context->decoder, context->target, &context->desc.base);
+   if (context->decoder->entrypoint == PIPE_VIDEO_ENTRYPOINT_ENCODE &&
+       context->desc.h264enc.p_remain == 1)
+      context->decoder->flush(context->decoder);
    pipe_mutex_unlock(drv->mutex);
    return VA_STATUS_SUCCESS;
 }