Add implementation for command 02: SUB_TO_LR
Implemented command 03: ADD_SUB_TO_LR
Implement AXWii commands 08/09, aka. "upload AUXA/AUXB and use it as a temp buffer to mix to MAIN L/R/S and AUXC L", aka. "what the fuck were they thinking?!"
Initialize the audiocommon mixer on the first write to DSPCR, even if DSP is not enabled. Fixes issue 6192.