audio: use of audio_route_{apply/reset}_and_update_path APIs

1) Update enable/disable device and route to use the new APIs.
   With this change, mixer controls will be updated in the order
   listed in mixer paths XML file.
2) update_mixer is now an unused var.

Change-Id: Ic0a8874e4a2080347cfa0c2e66af606a08a207a7
CRs-Fixed: 581453