[AVR32] Remove mii_phy_addr and eth_addr from eth_platform_data

The macb driver will probe for the PHY chip and read the mac address
from the MACB registers, so we don't need them in eth_platform_data
anymore.

Since u-boot doesn't currently initialize the MACB registers with the
mac addresses, the tag parsing code is kept but instead of sticking
the information into eth_platform_data, it uses it to initialize
the MACB registers (in case the boot loader didn't do it.) This code
should be unnecessary at some point in the future.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>