drm/amd/display: Continue with stream enable if DP link training fails.

Not necessarily a fatal problem - some monitors will recover and show
the stream anyway if link training fails.

Signed-off-by: Ken Chalmers <ken.chalmers@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>