Release buffers on MediaCodec#stop()

Release all buffers on Codec2 stop() in order to quick release in case
of using multiple Codec's from application.

Bug: 146679370
Test: atest CtsMediaTestCases -- --module-arg CtsMediaTestCases:size:small
Change-Id: I7a025c2d349442f93dbfab0bd1892df46229ef56