staging: octeon_ethernet: Convert to use device tree.

Get MAC address and PHY connection from the device tree.  The driver
is converted to a platform driver.

Signed-off-by: David Daney <david.daney@cavium.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Cc: linux-mips@linux-mips.org
Cc: devicetree-discuss@lists.ozlabs.org
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/3940/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>