net: Add ethernet support for MIPS Octeon

This patchs adds the ethernet & MDIO driver for the MIPS Octeon II / III
SoC platform. Please note that these drivers are based on the 2013
U-Boot version from Marvell and make use of the platform supported
helper functions for the ethernet functionality, including stuff like
SFP handling.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Ramon Fried <rfried.dev@gmail.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>