Add Audio Setting support for Si4713

[ShadowLight8]

While the Si4713 has quite a few audio settings that can be changed, the defaults seem to be pretty good already. Putting this out here for people to comment on if there are settings they specifically want.

[ShadowLight8]

Audio settings request: https://falconchristmas.com/forum/index.php/topic,8996.msg92698.html#msg92698

Ported from ShadowLight8/Si4713_FM_RDS#4