audio policy for concurrent capture.

First implementation of concurrent capture policy:
Initially, only capture for HOTWORD or FM TUNER sources or
re-route submix is allowed at the same time as any other capture.
Several capture clients can share the same input stream. In this case
active clients are sorted by audio source priority level and the input
path configuration and routing is driven by the highest priority
active source.

Bug: 22702906

Change-Id: Icbedfe001c6243ecad7a7b57ab78d893b2b97402