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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

Make it possible to access the ocotp registers before the ocotp device
is attached, by establishing a temporary mapping of the registers when
necessary. This is a temporary measure to keep progress moving; in the
long run we need better control over the order in which devices attach
(better than "the order they appear in the fdt dts source").

It turns out Freescale cleverly made the ocotp device compatible across
several different families of SoCs, so move it to the freescale directory
and prefix everything with fsl rather than imx6.