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

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

sys/dev: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

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.

Convert remaining {g,s}etenv->kern_{g,s}etenv
left over from r273174.

Reported by: bz

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

Start using the 'init_static_kenv()' API provided by r198561 to initialize
CFE environment variables.

Merge in new cfe environment passing of kenv for swarm/sibyte boards.

Submitted by: Neelkanth Natu