gpu: host1x: Set DMA mask

The default DMA mask covers a 32 bits address range, but host1x devices
can address a larger range on TK1 and TX1. Set the DMA mask to the range
addressable when we use the IOMMU to prevent the use of bounce buffers.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>