audio policy: refactor output and input opening

Refactor the way input and output streams are open so that common
logic is centralized in AudioOutputDescriptor and AudioInputDescriptor
classes.

This is in preparation of adding reference counting for ouputs and inputs
opened for a given profile.

Test: Manual
Change-Id: Id806e23077eb41f6398400ab40aeaa694c7d5603
7 files changed