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/

sys: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 3-Clause license.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

Special thanks to Wind River for providing access to "The Duke of
Highlander" tool: an older (2014) run over FreeBSD tree was useful as a
starting point.

Rationalize BSD license on sys/*/include/float.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.

Add C11 macros describing subnormal numbers to float.h.

Reviewed by: bde

Add parentheses where required. Without them, `sizeof LDBL_MAX'
is a syntax error and shouldn't be, while `1 FLT_ROUNDS' isn't a
syntax error and should be. Thanks to bde for the examples.

Fix the definition of FLT_EVAL_METHOD and some minor bugs.

Implement FLT_ROUNDS for arm. Some (all?) arm FPUs lack support for
dynamic rounding modes, but FPUless chips that use softfloat can support it
because everything is emulated anyway. (We presently have incomplete
support for hardware FPUs.)

Submitted by: Ian Lepore

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

- Import the HEAD csup code which is the basis for the cvsmode work.

Bring in a version of float.h more correct for softfloat.

Start all license statements with /*-

Make FLT_ROUNDS correctly reflect the dynamic rounding mode.

Import FreeBSD/arm kernel bits.
It only supports sa1110 (on simics) right now, but xscale support should come
soon.
Some of the initial work has been provided by :
Stephane Potvin <sepotvin at videotron.ca>
Most of this comes from NetBSD.