serrano: Add remote submix as global and fix sample rate

- Remote submix device is not added to available
  devices in audio policy manager. This is causing
  testRecordFromRemoteSubmix GTS test case failure
- Fix is to add it as part of global config so that
  it is added to available devices by default
- Only list 48000 Hz in supported sampling rates for
  remote submix output and input stream profiles to
  avoid mismatch between playback and capture.

Change-Id: Iaf1284af8149a0f3b7060266593799f493474aeb
serrano: Remove stuff taken care of by MSM init vendor lib

Change-Id: Ifca43105b3ea3490dd5a0d1eb21476c10243437b