Fixes #15140

If downstream is paused while the buffer is not full, continue
fetching. When the buffer is full, pause.

This function returns of list of hacks that are needed for codec
initialization, and also include IgnoreOmxDecoderPadding hack.

Remove OMX.MTK.VIDEO.DECODER.MPEG4 from blacklist since it only need a valid
CSD.

Rename it to pf_process_output. The output buffer is now dequeued/parsed
outside of the pf callback.

This commit also removes the decoder_NewPicture HACK to know if decoder is
flushing.

Split put_in into dequeue_in and queue_in.
Split get_out into dequeue_out and get_out

When the thread is cancelled, it will be exited before processing all input
blocks.