sys: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

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

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

hwpstate_amd: calculate power if P-state info comes from MSR

Reviewed by: markj
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D40140

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

cpufreq: Remove unused devclass arguments to DRIVER_MODULE.

Make CPU children explicitly share parent unit numbers.

Before this device unit number match was coincidental and broke if I
disabled some CPU device(s). Aside of cosmetics, for some drivers
(may be considered broken) it caused talking to wrong CPUs.

x86: clean up empty lines in .c and .h files

hwpstate(4): Ignore CurPstateLimit by default

Add a sysctl knob to allow users to re-enable it, and document the knob and
default in cpufreq.4. (While here, add a few unrelated updates to
cpufreq.4.)

It seems that the register value in some hardware simply reflects the
configured P-state. This results in an inadvertent and unintended outcome
where the P-state can only walk down, and then the driver becomes "stuck" in
the slowest possible P-state.

The Linux driver never consults this register, so that's some evidence that
ignoring the contents are relatively harmless.

PR: 234733
Reported by: sigsys AT gmail.com, Erich Dollanksy <freebsd.ed.lists AT
sumeritec.com>

hwpstate(4): Log a debug line when throttled

If we're going to throttle user requested P-states, we should at least produce
a debug log line indicating the surprising behavior.

PR: inspired by 234733

cpufreq(4): Add support for Intel Speed Shift

Intel Speed Shift is Intel's technology to control frequency in hardware,
with hints from software.

Let's get a working version of this in the tree and we can refine it from
here.

Submitted by: bwidawsk, scottph
Reviewed by: bcr (manpages), myself
Discussed with: jhb, kib (earlier versions)
With feedback from: Greg V, gallatin, freebsdnewbie AT freenet.de
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D18028