Support non PCM output requests with dynamic policy active

The audio policy previously failed to find available non PCM output
routes if any dynamic policy primary mixes were found. That
implementation failed the promise of fallback to the engine if there
are no output matches through explicit routing or dynamic policy.

Bug: 238286324
Test: atest audiopolicy_tests
Change-Id: I9420d3a4aceaa6cf874461b82f358032ee994949