dt-bindings: net: add the 10gbase-r connection type

Add 10gbase-r to the list of accepted PHY connection types between an
Ethernet device and a physical PHY. This is available as a valid
connection type since commit c114574e ("net: phy: add
PHY_INTERFACE_MODE_10GBASER")

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>