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

Remove /^/[*/]\s*\$FreeBSD\$.*\n/

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

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.

sys/dev: minor spelling fixes.

Most affect comments, very few have user-visible effects.

Consistently update to the MPI header set version 01.05.20 after r224761.
Requested by: mjacob

MFC after: 1 week

Update to MPI 1.5.16

Rev MPI spec to 1.05.09 level in preparation for SAS support.

MFC after: 1 month