sparc64: Enable 64-bit DMA

ATU 64bit addressing allows PCIe devices with 64bit DMA capabilities
to use ATU for 64bit DMA.

Signed-off-by: Tushar Dave <tushar.n.dave@oracle.com>
Reviewed-by: chris hyser <chris.hyser@oracle.com>
Acked-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>