ramips: fix AR8033 fiber operation

ramips: fix AR8033 fiber operation

It was reported AR8033 did not work in fiber operation mode on the ER-X.

While the earlier attempt of fixing this mitigated the issue of 1000
Base-X link mode not being supported, it also switched to the copper
page, breaking fiber operation altogether.

Extend the hack adding fiber operation so it does not switch to the
copper page. Also remove the part where the supported link mode bit for
1000 Base-X is removed, as this is required for fiber operation.

Signed-off-by: David Bauer <mail@david-bauer.net>