Reset the ISA DMA controller into a known state after a suspend. Primary
concern was reenabling the cascading DMA channel (4).

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

If this patch seems ok then I'll make another one for x86_64 (the only
other platform with ISA DMA AFAIK).

I couldn't find who was responsible for the i386 arch so I've cc:ed Linus.

Rgds
Pierre