va: investigate a way to dismiss unused memories after reverse playback
While reverse playback the number of buffer has to increase since the whole GOP has to be allocated before rendering. This might bring a lot of memory pressure, mainly in hardware accelerated decoding.
For example, in order to make more efficient the dmabuf-based memory allocation, va has an allocator's pool that stores all the created and released memories. But, after reverse playback (returning to normal playback) a lot of memories aren't required any more. It should be nice to find a mechanism to invalidate that memory cache.