fm: Restore fm on Speaker

During fm plaback even though routing device is changed from WHP
to SPK on UI, fm continues to route through WHP on targets with
shared backend for WHP and SPK. This is due to APM unaware of
routing device is change to SPK and selects WHP to play LL touch
tones causes all active usecase on SPK to move to WHP and fm
routes through WHP.

Change is to handle this scenario by re-routing fm on SPK once
standby is received for LL touch tones.

Change-Id: Ia503d4c134a3679fc2a51e2f9b7b8343e7b7cd1e