use generic DMA mapping code in powerpc V4

[Christian Zigotzky]

Hello Christoph,

I was able to compile 257002094bc5935dd63207a380d9698ab81f0775 from your 
Git powerpc-dma.6-debug today.

Unfortunately I don't see any error messages (kernel ring buffer) and I 
don't have a RS232 serial null modem cable to get them.

Cheers,
Christian