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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

Commit the first pass of the etherswitch support.

This is designed to support the very basic ethernet switch chip behaviour,
specifically:

* accessing switch register space;
* accessing per-PHY registers (for switches that actually expose PHYs);
* basic vlan group support, which applies for the rtl8366 driver but not
for the atheros switches.

This also includes initial support for:

* rtl8366rb support - which is a 10/100/1000 switch which supports
vlan groups;
* Initial Atheros AR8316 switch support - which is a 10/100/1000 switch
which supports an alternate vlan configuration (so the vlan group
methods are stubbed.)

The general idea here is that the switch driver may speak to a variety of
backend busses (mdio, i2c, spi, whatever) and expose:

* If applicable, one or more MDIO busses which ethernet interfaces can
then attach PHYs to via miiproxy/mdioproxy;

* exposes miibusses, one for each port at the moment, so ..

* .. a PHY can be exposed on each miibus, for each switch port, with all
of the existing MII/ifnet framework.

However:

* The ifnet is manually created for now, and it isn't linked into the
interface list, nor can you (currently) send/receive frames on this ifnet.
At some point in the future there may be _some_ support for this, for
switches with a multi-port, isolated mode.

* I'm still in the process of sorting out correct(er) locking.

TODO:

* ray's switch code in zrouter (zrouter.org) includes a much more developed
newbus API that covers the various switch methods, as well as a
capability API so drivers, the switch layer and the userland utility
can properly control the subset of supported features.

The plan is to sort that out later, once the rest of ray's switch drivers
are brought over and extended to export MII busses and PHYs.

Submitted by: Stefan Bethke <stb@lassitu.de>
Reviewed by: ray