arm: dts: Set custom names for cp110 master/slave MDIO buses

Implicitly Marvell MDIO driver uses DT node names for devices, but in this
case that is not unique.  Set MDIO device names for master/slave to
cpm/cps.

Signed-off-by: Alex Marginean <alexm.osslist@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>