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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

Switch TI platform support code from using FreeBSD's custom-baked DTS
files to vendor-provided ones. It should make easier to adopt platform
code to new revisions of hardware and to use DTS overlays for various
Beaglebone extensions (shields/capes).

Original dts filenames were not changed, they're now wrappers over dts
files provided by TI. So make sure you update .dtb files on your
devices as part of kernel update

GPIO addressing was changed: instead of one global /dev/gpioc0 there
are per-bank instances of /dev/gpiocX. Each bank has 32 pins so for
instance pin 121 on /dev/gpioc0 in old addressing scheme is now pin 25
on /dev/gpioc3

On Pandaboard serial console devices was changed from /dev/ttyu0 to
/dev/ttyu2 so you'll have to update /etc/ttys to get login prompt
on serial port in multiuser mode. Single user mode serial console
should work as-is

Differential Revision: https://reviews.freebsd.org/D2146
Reviewed by: rpaulo, ian, Michal Meloun, Svatopluk Kraus

Add PWM module driver for AM335x. Only eCAS subsystem is supported

Export function to configure eCAS submodule from another drivers.
It's used to control LCD panel backlight on AM335x EVM.