net: pcs-lynx: add support for 10GBASER

Add support in the Lynx PCS module for the 10GBASE-R mode which is only
used to get the link state, since it offers a single fixed speed.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>