[AudioPolicy][engineconfigurable] audioattribute should match audio_stream_assist first

if app play audio using uage AUDIO_USAGE_ASSISTANT,
attribute to stream should return audio_stream_assist first instead of audio_stream_music

audio_stream_assist:
 attrBuilder.setUsage(AudioAttributes.USAGE_ASSISTANT);
 attrBuilder.setContentType(AudioAttributes.CONTENT_TYPE_SPEECH);

audio_stream_music:
attrBuilder.setUsage(AudioAttributes.USAGE_ASSISTANT);

Signed-off-by: liuxiaoyu7 <liuxiaoyu7@xiaomi.com>
Change-Id: Ied2f0c076c53ecfd374fb58b48f0e5da07e3c7a8