target: ar71xx: add support for COMFAST CF-E316N v2 board

This adds full support (sans sysupgrading from vendor firmware) for the COMFAST
CF-E316N v2 (aka CF-E316V2, CF-E316N-V2 and CF-E316Nv2.0, no FCC ID) by
Shenzhen Four Seas Global Link Network Technology Co., Ltd (this company is
actively refusing to provide GPL'd sources for the OpenWrt version they ship
with the device, damn them).

Signed-off-by: Paul Fertser <fercerpav@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46852 3c298f89-4303-0410-b956-a3cf2f4a3e73