screenrecord: Enable SUBMIX_IN as well and cleanup on exit

While on Nexus 5/Nexus 7 (AOSP QCOM audio), trying to turn on
SUBMIX_IN fails and is not needed, it is required on Find 5
and N1 (CAF QCOM audio), or otherwise SUBMIX_OUT won't turn
on.
We also now release the audio routing as it wouldn't revive
the audio speakers otherwise.

Change-Id: I0f80a232304733e0b0a834b188b8cfa5b88915f3