arch: arm64: dts: lx2160a: describe the SerDes block #1

Describe the SerDes block #1 using the generic phys infrastructure. This
way, the ethernet nodes can each reference their serdes lanes
individually using the 'phys' dts property.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>