lantiq: xway_legacy: disable unused switches

lantiq: xway_legacy: disable unused switches

The xway_legacy subtarget only supports 5 devices. Most compiled
switch drivers are unused by any of these devices. The same drivers
are compiled into the xway subtarget. They were probably copied
from there when creating this subtarget.

Switches used by devices:
Arcadyan ARV4518PWR01   Realtek RTL8306SD
Arcadyan ARV4518PWR01A  Realtek RTL8306SD
Arcadyan ARV4520PW      Infineon ADM6996I
Arcadyan ARV4525PW      only PHY(IC+ IP101A)
Arcadyan ARV452CQW      Realtek RTL8306

The CONFIG_ETHERNET_PACKET_MANGLE symbol has also been disabled,
as it is only needed by the driver for AR8216.

Reduces kernel size by 19.9 kB.

Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>