sys: Remove ancient SCCS tags.

Remove ancient SCCS tags from the tree, automated scripting, with two
minor fixup to keep things compiling. All the common forms in the tree
were removed with a perl script.

Sponsored by: Netflix

sys: Remove $FreeBSD$: one-line .h pattern

Remove /^\s*\*+\s*\$FreeBSD\$.*$\n/

machine/in_cksum.h: don't include sys/cdefs.h

All consumers already do it and it was required on amd64 and i386
until recently (1c1bf5bd7c1e479a7889839b941f53e689aa2569).

Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D34932

Rationalize BSD license on sys/*/include/in_cksum.h

Remove the advertising clause from the Regents of the University of
California's license, per the letter dated July 22, 1999.

Update clause numbering.

Bring in the start of the arm64 kernel.

This is only the minimum set of files needed to boot in qemu. As such it is
missing a few things.

The bus_dma code is currently only stub functions with a full implementation
from the development tree to follow.

The gic driver has been copied as the interrupt framework is different. It
is expected the two drivers will be merged by the arm intrng project,
however this will need to be imported into the tree and support for arm64
would need to be added.

This includes code developed by myself, SemiHalf, Ed Maste, and Robin
Randhawa from ARM. This has been funded by the FreeBSD Foundation, with
early development by myself in my spare time with assistance from Robin.

Differential Revision: https://reviews.freebsd.org/D2199
Reviewed by: emaste, imp
Relnotes: yes
Sponsored by: The FreeBSD Foundation