New sound driver support with initial support for the SN76489 chip
New build configuration entry:
* SN76489ENABLE
Ports are currently locked in with:
* SN76489_PORT_LEFT .EQU $FC ; PORTS FOR ACCESSING THE SN76489 CHIP (LEFT)
* SN76489_PORT_RIGHT .EQU $F8 ; PORTS FOR ACCESSING THE SN76489 CHIP (LEFT)