sparc32 fix spurious dma interrupts v2

sparc32 fix spurious dma interrupts v2

Don't raise irq when not enabled.
Raise irq on enabling if DMA_INTR is set
Don't clear irq unless it was raised by DMA, as there are other irq sources
Don't set DMA_INTR bit spuriously.

v1->v2:
 - Don't clear irq unless it was raised by DMA
 - Raise irq on enabling if DMA_INTR is set
 - Assume revertion of 787cfbc432bf1d353a77cbdb613754f3963371a3

Signed-off-by: Artyom Tarasenko <atar4qemu@gmail.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>