powerpc: Use the newly added get_required_mask dma_map_ops hook

Now that the generic code has dma_map_ops set, instead of having a
messy ifdef & if block in the base dma_get_required_mask hook push
the computation into the dma ops.

If the ops fails to set the get_required_mask hook default to the
width of dma_addr_t.

This also corrects ibmbus ibmebus_dma_supported to require a 64
bit mask.  I doubt anything is checking or setting the dma mask on
that bus.

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-kernel@vger.kernel.org
Cc: benh@kernel.crashing.org
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/dma-iommu.c

@@ -90,7 +90,7 @@ static int dma_iommu_dma_supported(struct device *dev, u64 mask)
 		return 1;
 }
 
-u64 dma_iommu_get_required_mask(struct device *dev)
+static u64 dma_iommu_get_required_mask(struct device *dev)
 {
 	struct iommu_table *tbl = get_iommu_table_base(dev);
 	u64 mask;
@@ -111,5 +111,6 @@ struct dma_map_ops dma_iommu_ops = {
 	.dma_supported	= dma_iommu_dma_supported,
 	.map_page	= dma_iommu_map_page,
 	.unmap_page	= dma_iommu_unmap_page,
+	.get_required_mask	= dma_iommu_get_required_mask,
 };
 EXPORT_SYMBOL(dma_iommu_ops);