NOTE 1
Since we do not have any mechanism to set the parent device
for a platform one (we do not have device tree), we can't set
the DMA mask.

Perhaps what we should do is to have the actual dma engine to set
this value. Then the problem will move to the DMA engine: how to get
its parent device

Signed-off-by: Federico Vaga <federico.vaga@cern.ch>