Adds two more ethernet interface to 83xx

Added as a convenience for other platforms that uses MPC8360 (has 8 UCC).
Six eth interface is chosen because the platform I am using combines
UCC1&2 and UCC3&4 as 1000 Eth and the other four UCCs as 10/100 Eth.

Signed-off-by: Richard Retanubun <RichardRetanubun@RugggedCom.com>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>