MIPS: Lantiq: Add support for xRX220 SoC

Signed-off-by: Hauke Mehrtens <hauke.mehrtens@lantiq.com>
Acked-by: John Crispin <blogic@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11394/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>