MIPS: Lantiq: Add support for gphy firmware loading for ar10 and grx390

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/11389/
Patchwork: https://patchwork.linux-mips.org/patch/11398/


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