This adds emulation for the dual OPL2 FM synthesis chip configuration to the
supported hardware OPL3 options: RetroWave OPL3 and OPL3LPT. This enables
stereo AdLib playback for SCI (and possibly other engines) on these devices.
This was already implemented for the OPL3 emulators (Dosbox and Nuked) and
ALSA. Generic code has been added to the OPL class to add similar emulation
for the other OPL3 options; this can also be easily added to any future OPL3
hardware or emulators which do not already have dual OPL2 support.
ca111f3170