Merge from projects/mips to head by hand:
Merge support files for the Atheros AR71xx (and soon AR9xxx)
processors, except files from sys/conf and sys/mips/conf. This work
was done primarily by Olecksandr Tymoshenko and works on the
RouterStation and RouterStation PRO. Other AR71xx-based boards have
been reported as working as well (RouterBoard, for example).