hal: allow VOIP standby to enable correct device for subsequent usecases

When an MT call is received during a VOIP call, the VOIP could be standby
but not closed, since the standby is ignored, the VOIP use case is left with
active, ringtone will be played on the device of VOIP stream.
Allow putting the VOIP into standby state to release the VOIP use case when it's
not active. Then audio route for susequent usecases can be switched to the
expected device.

Change-Id: I735277d21dbdde7117eb7a4f765993e23cdea45c
CRs-Fixed: 1033873