sys: Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

usb: Remove unused devclass arguments to DRIVER_MODULE.

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.

The MII layer shouldn't care about administrative status of an
interface. Make MII drivers forget about 'struct ifnet'.

Later plan is to provide an administrative downcall from ifnet
layer into drivers, to inform them about administrative status
change. If someone thinks that processing MII events for an
administratively down interface is a big problem, then drivers
would turn MII processing off.

The following MII drivers do evil things, like strcmp() on
driver name, so they still need knowledge of ifnet and thus
include if_var.h. They all need to be fixed:

sys/dev/mii/brgphy.c
sys/dev/mii/e1000phy.c
sys/dev/mii/ip1000phy.c
sys/dev/mii/jmphy.c
sys/dev/mii/nsphy.c
sys/dev/mii/rgephy.c
sys/dev/mii/truephy.c

Sponsored by: Netflix
Sponsored by: Nginx, Inc.

Fix compiler warnings, mostly signed issues,
when USB modules are compiled with WARNS=9.

MFC after: 1 weeks

Use DEVMETHOD_END.

- Follow the lead of dcphy(4) and pnphy(4) and move the reminder of the PHY
drivers that only ever attach to a particular MAC driver, i.e. inphy(4),
ruephy(4) and xlphy(4), to the directory where the respective MAC driver
lives and only compile it into the kernel when the latter is also there,
also removing it from miibus.ko and moving it into the module of the
respective MAC driver.
- While at it, rename exphy.c, which comes from NetBSD where the MAC driver
it corresponds to also is named ex(4) instead of xl(4) but that in FreeBSD
actually identifies itself as xlphy(4), and its function names accordingly
for consistency.
- Additionally while at it, fix some minor style issues like whitespace
in the register headers and add multi-inclusion protection to inphyreg.h.