nuplayer: start or stop audio sink from renderer only

NuPlayerRenderer maintains the state of AudioSink, and based on that
data is written to the audioSink.

But in certain cases, AudioSink is directly accessed by NuPlayerDriver,
which causes a mismatch in the state maintained in the renderer.

Ensure that audiosink is start/stop from renderer only.

CRs-Fixed: 840811
Change-Id: I663c876a7e6d529aabb44fc8768cc657a1b228d0