[Enhancement] Nuked OPN-Mod support

[freq-mod]

Original discussion. Nuked OPN-Mod, in short, is a modification of Nuked OPN2 by @jpcima that attempts to emulate YM2608 FM block. Accuracy, therefore is very high, SSG-EG works perfectly as well.

Only minor inconviniences:

• there are still some code pieces that refer to YM2612 (channels 6 DAC mode) iirc
  bit conversion/phase interference (??) distortion noise that is not present on the real chip fixed already

Still, it is the close second best thing to a real OPNA hardware passthrough.

P.S. As for PMDWin, bad news, it is discontinued; newer versions of this library (0.37 onward) are based off Neko Project 2 fmgen. IMO there is no reason keeping such a broken emulator here, as MAME 2608 and fmgen aren't that heavy at all anyway.