amd-xgbe: Use dma_set_mask_and_coherent to set DMA mask

Use the dma_set_mask_and_coherent function to set the DMA mask rather
than setting the DMA mask fields directly.  This was originally done
to work around a bug in the arm64 DMA support when RAM started above
the 4GB boundary which has since been fixed.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>