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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

Add support for Freescale Vybrid Family VF600 heterogeneous
ARM Cortex-A5/M4 SoC (M4 core is not used in this work).

Support includes device drivers for:
- NAND Flash Controller (NFC)
- USB Enhanced Host Controller Interface (EHCI)
- General-Purpose Input/Output (GPIO)
- Universal Asynchronous Receiver/Transmitter (UART)

Also supported:
- Generic Interrupt Controller (GIC)
- MPCore timer
- ffec ethernet driver

Reviewed by: ray
Approved by: cognet (mentor)