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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

Remove "All Rights Reserved" from FreeBSD Foundation sys/ copyrights

These ones were unambiguous cases where the Foundation was the only
listed copyright holder (in the associated license block).

Sponsored by: The FreeBSD Foundation

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

Reformat indentation to match other imx5/6 register definition headers, and
tweak some comments. No functional changes.

sys/arm: 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.

Rename sysctl node hw.imx6 to hw.imx. Move its definition to imx_machdep.c
so that code shared between imx5 and imx6 can work with OIDs under that node.

Add last_reset_status (integer) and last_reset_reason (string) OIDs that
provide info about the last chip reset (power-on, software reset, watchdog
timeout).

Add compatible strings for all the hardware this driver works with.

Also, move the READ/WRITE bus space access macros from the header into the
source file, and rename them to RD2/WR2 to make it clear they're 16-bit
accessors. (READ/WRITE just don't seem like good names to be in a public
header file.)

Update copyright date.

Integrate Efika MX project back to home.

Sponsored by: The FreeBSD Foundation