add uboot-oxnas

This adds support for the oxnas target in U-Boot 2014.04
History can be found at https://github.com/kref/u-boot-oxnas up to 2013.10
changes from 2013.10 to 2014.04 can be followed at
https://gitorious.org/openwrt-oxnas

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43389 3c298f89-4303-0410-b956-a3cf2f4a3e73