MIPS: BCM47XX: add Microsoft MN-700 and Asus WL500G

This patch adds detection for the Microsoft MN-700 and the Asus WL500G
router. This is based on some old code from OpenWrt.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Cc: zajec5@gmail.com
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7490/


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