Allow 8 bit volume for YM2610 ADPCM-B
Remove sample mode macro in YM2610, it's always enabled and seperated channels.
TODO: ADPCM-B is still not implemented, FM Channel 2 is silenced in extended channel 3 configuration
as of now compound systems (Genesis and Arcade) are translated to
separate chips.
this improves audio quality and makes things easier.
it also allows you to change the volume of each chip on a Genesis.
also adds SegaPCM system with 16 channels!
