Switchtec hardware supports 64-bit DMA, so set the correct DMA mask.  This
allows the CMA to allocate larger buffers for memory windows.
Signed-off-by: NBoris Glimcher <Boris.Glimcher@emc.com>
Signed-off-by: NWesley Sheng <wesley.sheng@microchip.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Reviewed-by: NLogan Gunthorpe <logang@deltatee.com>