netdev: mdio-octeon.c: Convert to use device tree.

netdev: mdio-octeon.c: Convert to use device tree.

Get the MDIO bus controller addresses from the device tree, small
clean up in use of devm_*

Remove, now unused, platform device setup code.

Signed-off-by: David Daney <david.daney@cavium.com>
Acked-by: David S. Miller <davem@davemloft.net>
Cc: linux-mips@linux-mips.org
Cc: devicetree-discuss@lists.ozlabs.org
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/3938/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>