Add support for the Black Swift board:
http://www.black-swift.com/

Took relevant parts and slightly adapted from:
https://github.com/blackswift/openwrt/blob/master/bsb.patchSigned-off-by: Bruno Randolf <br1@einfach.org>

git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@46674 3c298f89-4303-0410-b956-a3cf2f4a3e73