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

Remove /^/[*/]\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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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.

Modify the FreeBSD USB kernel code so that it can be compiled directly
into the FreeBSD boot loader, typically for non-USB aware BIOSes, EFI systems
or embedded platforms. This is also useful for out of the system compilation
of the FreeBSD USB stack for various purposes. The USB kernel files can
now optionally include a global header file which should include all needed
definitions required to compile the FreeBSD USB stack. When the global USB
header file is included, no other USB header files will be included by
default.

Add new file containing the USB stack configuration for the
FreeBSD loader build.

Replace some __FBSDID()'s by /* $FreeBSD$ */ comments. Now all
USB files follow the same style.

Use cases:
- console in loader via USB
- loading kernel via USB

Discussed with: Hiroki Sato, hrs @ EuroBSDCon

Remove unneeded includes of <sys/linker_set.h>. Other headers that use
it internally contain nested includes.

Reviewed by: bde

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

- Make struct usb_xfer opaque so that drivers can not access the internals
- Reduce the number of headers needed for a usb driver, the common case is just usb.h and usbdi.h

s/usb2_/usb_|usbd_/ on all function names for the USB stack.

s/usb2_/usb_/ on all typedefs for the USB stack.

Move the new USB stack into its new home.