Remove Cavium/Econa CNS11xx support.

This port hasn't been updated since it was committed, apart from
housekeeping. There's no known users, and the known hardware for
this port is too thin to run FreeBSD/arm these days well.

This also removes the last armv4 port. We've had no reports of armv4
systems working since FreeBSD 8. All the kernel support for armv4 has
not been removed since it's too intertwined with armv5 support (which
remains in the tree).

RelNotes: Yes
No objection from: arm@