audio policy: enable more than one sink per audio patch.

Allow creation of audio patches with more than one sink.
More than one sink is enabled when:
- Connecting an input device to output devices on the same audio HW module.
- Connecting an output mix to output devices on the same audio HA module.

All other patches are limited to one sink.

Bug: 16879363.
Change-Id: I95be6948ef29df64e51e5b8ace38c2db7f3e89f2