drm/amd/display: re-enable audio after LT test

[Description]
Audio should be attached to the same pipe once it is attached.
We will not remove audio endpoint in disable stream.
We will reeanble the audio after automated link training test

Signed-off-by: Wenjing Liu <Wenjing.Liu@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>