"de-initialize" DMA channel 0 target after WRAM pre-game init

This actually triggered a sort of copy protection scheme by performing
DMA to an uninitialized destination address (by game code), which in
fact WAS initialized by the sd2snes menu, overwriting WRAM data
including the stack.
MSU1: make sure to stop audio playback on reset

Users reported static noise after soft resetting MSU software
Add cx4+uPD7725 variable speeds
Merge branch 'borti4938-develop' into develop
Merge branch 'develop' of ssh://github.com/mrehkopf/sd2snes into develop