AudioFlinger: allow shared record audio history for fast capture

Enable shared audio history when a fast capture thread is present.
In this case, the fast capture thread is preserved but no fast record client
is allowed.

Bug: 186894758
Bug: 185972521
Test: atest AudioRecordSharedAudioTest
Change-Id: I78b11a35513c771e6966c533c2fd094c05a48ead