OF: MIPS: lantiq: implement OF support

Activate USE_OF, add a sample DTS file and convert the core soc code to OF.

Signed-off-by: John Crispin <blogic@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: devicetree-discuss@lists.ozlabs.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3803/


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