ramips: add support for Sparklan WCR-150GN board

This patch adds support for Sparklan WCR-150GN board.
Network configuration should be tweaked to make it work fully. The
reason it's not in this patch is that ramips target should be modified
to support different /etc/config/network files for different boards.

Signed-off-by: Roman Yeryomin <roman@advem.lv>

SVN-Revision: 22658