engine configurable: AUDIO_SOURCE_UNPROCESSED aligment with legacy

This patch realigns the configurable version of the engine
with the legacy one with regards the new AUDIO_SOURCE_UNPROCESSED.

This is required to pass the Audio Frequency Line CTS test.

Bug: 29096641

Change-Id: I88abf91807bf66671ad3da6030d6aa6487cf4c54
Signed-off-by: Di Folco, Neil <neil.di.folco@intel.com>