Renumber copyright clause 4

Renumber cluase 4 to 3, per what everybody else did when BSD granted
them permission to remove clause 3. My insistance on keeping the same
numbering for legal reasons is too pedantic, so give up on that point.

Submitted by: Jan Schaumann <jschauma@stevens.edu>
Pull Request: https://github.com/freebsd/freebsd/pull/96

Bring over my FreeBSD modifications for the AR9300 HAL to make it
work in FreeBSD.

This is still heavily a work in progress but I'd rather it start
shipping in -HEAD sooner rather than later.

This doesn't (yet) link it into the build system either for a static
kernel or as a module; that will come later (after many, many make universe
tests.)