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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

Move KHELP_DECLARE_MOD_UMA later in the boot

Both KHELP_DECLARE_MOD_UMA and the kernel linker SYSINIT to find
in-kernel modules run at SI_SUB_KLD, SI_ORDER_ANY. As the former
depends on the latter running first move it later in the boot,
to the new SI_SUB_KHELP. This ensures KHELP_DECLARE_MOD_UMA
module SYSINIT functions will be after the kernel linker.

Previously we may have received a panic similar to the following if
the order was incorrect:

panic: module_register_init: module named ertt not found

Reported by: bob prohaska <fbsd AT www.zefox.net>
Discussed with: imp, jhb
Sponsored by: The FreeBSD Foundation

sys/sys: 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.

Now that the necessary infrastructure is in place to ensure hhook points which
register after a khelp module will get hooked, move khelp module initialisation
to the earlier SI_SUB_KLD stage.

MFC after: 1 week

Remove some duplicate code by making KHELP_DECLARE_MOD() a wrapper around
KHELP_DECLARE_MOD_UMA().

MFC after: 3 days

Use the full and proper company name for Swinburne University of Technology
throughout the source tree.

Requested by: Grenville Armitage, Director of CAIA at Swinburne University of
Technology
MFC after: 3 days

- Introduce the Hhook (Helper Hook) KPI. The KPI is closely modelled on pfil(9),
and in many respects can be thought of as a more generic superset of pfil.
Hhook provides a way for kernel subsystems to export hook points that Khelp
modules can hook to provide enhanced or new functionality to the kernel. The
KPI has been designed to ensure hook points pose no noticeable overhead when
no hook functions are registered.

- Introduce the Khelp (Kernel Helpers) KPI. Khelp provides a framework for
managing Khelp modules, which indirectly use the Hhook KPI to register their
hook functions with hook points of interest within the kernel. Khelp modules
aim to provide a structured way to dynamically extend the kernel at runtime in
an ABI preserving manner. Depending on the subsystem providing hook points, a
Khelp module may be able to associate per-object data for maintaining relevant
state between hook calls.

- pjd's Object Specific Data (OSD) KPI is used to manage the per-object data
allocated to Khelp modules. Create a new "OSD_KHELP" OSD type for use by the
Khelp framework.

- Bump __FreeBSD_version to 900028 to mark the introduction of the new KPIs.

In collaboration with: David Hayes <dahayes at swin edu au> and
Grenville Armitage <garmitage at swin edu au>
Sponsored by: FreeBSD Foundation
Reviewed by: bz, others along the way
MFC after: 3 months