audio HAL: support multiple active input streams

Implement support for more than one active input streams.
New implementation is limited to one active stream per capture use
case as there is one PCM ALSA device per front end and use case.
Note that the number of active sound trigger sessions is limited by the
soundtrigger implementation, not the number of PCM ALSA devices.
We do not enforce a max number of open streams per use case as this is
done by the audio_polcy_configuration file.

Bug: 111438757
Test: manual audio smoke tests for capture.
Change-Id: I1a372bca154d1ee034526f2b6b3ddeeae93a71f2