powerpc: Change archdata dma_data to a union

Sometimes this is used to hold a simple offset, and sometimes
it is used to hold a pointer.  This patch changes it to a union containing
void * and dma_addr_t.  get/set accessors are also provided, because it was
getting a bit ugly to get to the actual data.

Signed-off-by: Becky Bruce <beckyb@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/platforms/cell/beat_iommu.c b/arch/powerpc/platforms/cell/beat_iommu.c
index 93b0efd..39d361c 100644
--- a/arch/powerpc/platforms/cell/beat_iommu.c
+++ b/arch/powerpc/platforms/cell/beat_iommu.c
@@ -77,7 +77,7 @@
 static void celleb_dma_dev_setup(struct device *dev)
 {
 	dev->archdata.dma_ops = get_pci_dma_ops();
-	dev->archdata.dma_data = (void *)celleb_dma_direct_offset;
+	set_dma_offset(dev, celleb_dma_direct_offset);
 }
 
 static void celleb_pci_dma_dev_setup(struct pci_dev *pdev)