ramips: Use generic board detect for GnuBee devices

ramips: Use generic board detect for GnuBee devices

This is a port of an old commit from mkresin's tree:

09260cdf3e9332978c2a474a58e93a6f2b55f4a8

This has the potential to break sysupgrade but it should be fine as
there is no stable release of LEDE or OpenWrt that support these devices.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
(cherry picked from commit 9685f3978795727ac99d5d20a4af16c808b1e24b)