audio: add flag for stream suspend removal

Add a flag to gate removal of stream suspend mechanism.
The control logic in audio policy manager is buggy due to the introduction
of spatializer output on A2DP HAL module and the suspend mechanism is not
useful anymore given how SCO / A2DP mutual excusion is now managed.

Flag: com.android.media.audioserver.remove_stream_suspend
Bug: 409706525
Test: make
Change-Id: I5d31ac4a96bd5bbf63eb3f32138b2df76244c826