nuplayer: acquire wakelock during offload pause timeout

Nuplayer utilizes AMessage to post pause timeout message. Unlike timed
event queue used by awesome player, AMessage won't hold wakelock, which
results in tear down doesn't happen after kOffloadPauseMaxUs since ARM
cores are sleeping. As a result, audio output driver won't be closed
which blocks XO shutdown.

Implement wakelock request in Nuplayer render.

CRs-Fixed: 785828
Change-Id: I3d11fef633e3f2783f4aa31e71285e2fa09d234c