av1parse: Always copy the OBU to cache.

av1parse: Always copy the OBU to cache.

The current optimization when input align and out out align are
the same is not very correct. We simply copy the data from input
buffer to output buffer, but we failed to consider the dropping of
OBUs. When we need to drop some OBUs(such as filter out the OBUs
of some temporal ID), we can not do simple copy. So we need to
always copy the input OBUs into a cache.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1979>