portaudio: refactor to support split stream design

Allows the start/stop of individual streams as well as both input
and output simultaneously. When both streams are to be started,
full duplex mode is attempted first.

Resets device indices to -1 in the case that the host api has
changed, or if the dring audio config is scrapped somehow.

Change-Id: I1655a34d2111222b6add19f1b36b53bc4a2838ec