PPC4xx (Sequoia): Fix Ethernet "remote fault" problems

Every now and then a Sequoia board (or equivalent hardware) had
problems connecting to a Gigabit capable network interface.

There were differences in the PHY setup between Linux and U-Boot.

This patch fixes the problem. Apparently "remote fault" is being set,
which signals to some devices (on the other end of the cable) that a
fault has occurred, while other devices ignore it. I believe the RF bit
was causing the issue, but I removed T4 also, to match up with Linux.

Signed-off-by: Mike Nuss <mike@terascala.com>