mips: octeon: ebb7304: Enable ethernet support

mips: octeon: ebb7304: Enable ethernet support

This patch enables the Kconfig symbols needed for full ethernet support
on the EBB7304. Also the PHY autonegotiation timeout is increased, as
the default 5 seconds are sometime a bit short. With this, ethernet can
be used on this board. Here an example of a tftp load:

=> tftp ffffffff81000000 big
ethernet-mac-nexus@11800e0000000 Waiting for PHY auto negotiation to complete....... done
Using ethernet-mac-nexus@11800e0000000 device
TFTP from server 192.168.1.5; our IP address is 192.168.1.243
Filename 'big'.
Load address: 0xffffffff81000000
Loading: ##################################################  10 MiB
         13.2 MiB/s
done
Bytes transferred = 10485760 (a00000 hex)

Signed-off-by: Stefan Roese <sr@denx.de>