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

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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: clean up empty lines in .c and .h files

sys/sys: 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.

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.

o Don't make the SER_INT_* defines visible to userland. They
are related to internals, not user-visible state.
o Add a typedef for serdev_intr_t and protect it with !LOCORE.

MFp4:
o Add defines for the 5 interrupt sources typical for serial devices.
These defines can be used for more finegrained interrupt handling
between drivers that cooperatively handle multiple serial ports.
o Add defines for the various bitmasks applicable when all information
is passed between drivers as a single integral.

MFp4:
style(9): <tab> after #define

Make the relationship between modem control bits and their delta cousins
public.

Add a tty-independent include file for definitions pertaining to serial
ports.

Define the most commonly used modem signals, and delta-bit definitions
for them.