Convert OPN to OPL series, lose FM3ex extra channel

[denjhang]

There are many OPNs that use FM3ex channels. The third channel of FM is split into multiple channels for use. I hope this feature can be handled correctly.

[okaxaki]

There are many good music using FM3-ext. I hope too but It's a bit complicated, so I'll get to it when I get some time.