MIPS: lantiq: remove bogus define

Signed-off-by: Luka Perkov <luka@openwrt.org>
---
This should be "fixup"-ed with following commit:

f855666 MIPS: add support for Lantiq XWAY SoCs
MIPS: lantiq: update openwrt configuration

Signed-off-by: Luka Perkov <luka@openwrt.org>
---
This should be "fixup"-ed with following commit:

821ff0e MIPS: lantiq: add default openwrt config