NuPlayer: Teardown sequence for pcm offload

On a teardown event, follow proper shutdown sequence
if the decoder instance type is not passthrough.

This is needed to ensure NuPlayerDecoder, MediaCodec do
not enter an invalid state due to forced clear while
handling a teardown event.

CRs-Fixed: 916643
Change-Id: Ied5df07dc8567974ef02e3a0bb415795f31f2ed2