use generic DMA mapping code in powerpc V4

[Christian Zigotzky]

Hi Christoph,

Mario successfully tested a kernel from your Git [1] on his T2080rdb today.

Link to the log: 
https://gitlab.com/oshw-powerpc-notebook/T2080customizations/blob/master/kernel/dma_fix/kernel_dma_fix_log.txt

He wrote:

Please, note that all of the above kernel runs just fine with the T2080rdb, however did not had the time to test extensively (tested: login into MATE graphical desktop environment, used ArctiFox for opening couple of websites, then played Neverball).

——

Cheers,
Christian

[1] http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/powerpc-dma.6