Layerscape MACs support 25Gbps network speed with dpmac "CAUI" mode.
Add the mappings between DPMAC_ETH_IF_* and HY_INTERFACE_MODE_*, as well
as the 25000 mac capability.

Tested on SolidRun LX2162a Clearfog, serdes 1 protocol 18.
Signed-off-by: Josua Mayer <josua@solid-run.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>