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

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

tws: fix "set but not used" in the tws driver

With __diagused, these warnings were still emitted since INVARIANTS was
defined but TWS_DEBUG was not.

Fixes: a21f086a3316 ("Fix "set but not used" in the tws driver")
Differential Revision: https://reviews.freebsd.org/D33784

tws: clean up empty lines in .c and .h files

Remove support for versions prior to FreeBSD 7.0 from twa(4)

This was for pre-7.0 CAM support. Neither the CAM nor the busdma
changes over the years have not been ifdef'd. The code cannot build
on 6.x anymore. Support for 6.4 ended in 2010, so remove them.

sys/dev: 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.

Don't expose a constant array into global namespace.

Reported by: Ruslan Yakovlev <quazi bk ru> via yongari
MFC after: 3 days

Add the 9750 SATA+SAS 6Gb/s RAID controller card driver, tws(4). Many
thanks for their contiued support to FreeBSD.

This is version 10.80.00.003 from codeset 10.2.1 [1]

Obtained from: LSI http://kb.lsi.com/Download16574.aspx [1]