generic: at803x: mask 1000 Base-X link mode

generic: at803x: mask 1000 Base-X link mode

AR8031/AR8033 have different status registers for copper
and fiber operation. However, the extended status register
is the same for both operation modes.

As a result of that, ESTATUS_1000_XFULL is set to 1 even when
operating in copper TP mode.

Remove this mode from the supported link modes, as this driver
currently only supports copper operation.

Signed-off-by: David Bauer <mail@david-bauer.net>
Signed-off-by: maurerr <mariusd84@gmail.com>